Cancer in Domesticated Animals

Humans aren't the only ones affected by cancer. This section contains information detailing cancer in domesticated animals. If the animal/cancer type in which you are interested is not yet presented, please check back because we add new information regularl. Further information on the topics on this page can also be found in most introductory biology textbooks, we recommend the textbook, Campbell Biology, 11th edition.1

Cancer in Pets

According to the American Veterinary Medical Association (AVMA), cancer causes almost 50% of deaths in pets over the age of 10. Some common types of cancers in pets include: skin, breast, head and neck, lymphomaA cancer arising in the lymphatic system. The white blood cells affected are part of the body's immune system. The lymphatic system is a large network of vessels that carry fluid and cells of the immune system around the body. Lymph nodes are regional collection centers in the lymphatic system. See also, 'lymphatic system'., leukemiaA cancer affecting the cells that develop into white or red blood cells. Both of these cell types originate from stem cells in bone marrow. Red blood cells function to carry oxygen to our tissues and the white cells (leukocytes) are part of our immune system. The cancerous cells often accumulate in the blood., testicular, abdominal, and bone. Examples of cancers commonly found in pets that are also commonly found in humans are lymphoma, melanoma, and osteosarcomaCancer of the bone. Osteosarcomas are derived from osteoblasts, cells that line the outside of bones. It is most common among children and young adults and affects males more than females.. 2, 3

Of the two most common household pets, dogs tend to get cancer at a higher rate than cats. The cancer may be treatable depending on cancer type. Cancer treatment options for dogs and cats are similar to those for humans. Surgery, radiationIn cancer biology: A cancer treatment in which high energy beams are used to kill cancer cells. Radiation can also cause genetic damage that can lead to cancer. As an example, skin cancer is believed to be greatly increased by exposure to ultraviolet (UV) radiation from the sun. therapy, chemotherapyTreatment of cancer patients with anticancer drugs. Commonly called 'chemo'. These drugs work by attacking cell growth or division. Often these agents are used in combination to take advantage of their different modes of attack on cell division., and immunotherapyA treatment for a disease (including cancer) that involves the modulation of the immune system. Treatments include the administration of cytokines (proteins produced by cells of the immune system) and vaccinations. are all considered and will usually result in less side effects in animals than in humans. Veterinarians will tailor treatment dosages to optimize efficacy and minimize side effects. 3

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Cancer in Cats

Cancer in Cats

 

Cats are susceptible to a variety of cancers.  Among the most common are lymphoma, squamous cell carcinoma (skin cancer), mammary cancer, mast cell tumors, oral tumors, fibrosarcoma (soft tissue cancer) , osteosarcoma (bone cancer), respiratory carcinoma, intestinal adenocarcinoma, and pancreatic/liver adenocarcinoma.  The disease has become so prevalent that it is now the most common cause of death in cats.4


Certain breeds are more prone to certain cancers than others.  Signs and symptoms differ depending on the type and stage of the cancer.  Detection and diagnosis requires some detective work.  Tumors that are visible and/or detectable by touch are most easily identified.   Vets often perform additional tests to make an accurate diagnosis.  Along with a physical exam, they may perform blood and urine tests, cytology, imaging and biopsies.

Treatment options vary and include surgery, chemotherapy, radiation, immunotherapy, photodynamic therapy, or a combination of these.  In many cases, cancer can be successfully treated.  Early detection and diagnosis is critical.  Regular visits to the veterinarian can help prevent and manage cancer. The American Veterinary Medical Association recommends twice-a-year wellness exams for all cats.5  Because the causes of cancer in cats are similar to those in humans, risk can be reduced by lowering the animal's exposure to harmful carcinogens, including tobacco smoke.6

 

 

Feline Leukemia and the Feline Leukemia Virus

Overview and Transmission

In humans, some viruses can lead to cancer. An example is human papilloma virus (HPV) which is the causative agent of most cases of cervical cancer. Viral infection can also lead to cancer in animals. Feline leukemia (FeLV; informally known as "Fee-Leuk") is an RNAAlso: ribonucleic acid. RNA is a polymer comprised of the nucleotides A, C, G and U. RNA is the working form of our genetic information. RNA is produced via the process of transcription. Some RNA is used to help build ribosomes (rRNA) and some (mRNA) are used to guide the formation of proteins. Other forms of RNA are used to perform specialized functions in the nucleus. virus (a retrovirusA virus that has RNA as its genetic material. Since the most common genetic material for organisms is DNA, these viruses are sort of backwards, hence the name retro-virus. During infection retroviruses may rarely take some cellular DNA with them when they leave the cell. Some of the first oncogenes were discovered because they were carried by retroviruses. These retroviruses were found to cause cancer and it was later shown to be due to the presence of the altered oncogene in the virus.) that infects less than 2% of healthy, domestic cats in the U.S.7, 8 Infection is more prevalent in high-risk populations (i.e. cats with outdoor access and/or frequent social interactions).7

The virus is spread from one cat to another via saliva, nasal secretions, feces, and milk.9, 10 It is transmitted during various forms of contact, from friendly grooming to not-so-friendly biting. The virus can also be passed to a developing kitten during pregnancy. The age and time of infection affect the progression and clinical outcome of the virus. Kittens are more likely to be infected and more likely to develop more severe complications.11 In most cases, FeLV initially infects lymphocytes in the back of the throat (oropharynx), which travel to the bone marrow, where virally infected cells are produced very rapidly.12

In most environments, the Feline leukemia virus cannot survive for long outside of the host. It can be 'killed' (made harmless) with soap and disinfectants. At this time, studies show no evidence that FeLV can be transmitted from infected cats to humans.13 However, because FeLV positive cats may carry other diseases, infants, elderly individuals, and immunosuppressed individuals may want to avoid contact.

 

Symptoms

Infected animals may develop anemia, lymphoma, and other conditions. The FeLV-C subtype binds to and impedes the function of a heme transport proteinOne of the four basic types of biomolecule. Proteins are polymers made up of strings of amino acids. Proteins serve many functions in organisms including transport of molecules, structure, cell adhesion and as signaling molecules such as hormones. Many transcription factors, including p53 and Rb are proteins. on the surface of developing red blood cells. The result is a decrease in red blood cell numbers (anemia).14, 15 Signs of anemia in cats include paleness of the skin, tongue, gums, and mucous membranes surrounding the eye. FeLV- induced lymphomas are some of the most frequent tumors seen in cats. Symptoms depend on the location of the tumor, and may include weight loss, rough hair coat, loss of appetite, vomiting, diarrhea, respiratory distress, swelling of the lymph nodesA grape-like cluster of lymphatic tissue. Lymph nodes (or lymph glands) filter the lymph fluid that flows through the lymphatic system. Lymph nodes collect fluid from discrete regions of the body and are often examined for the presence of metastasizing cancer cells. and more. FeLV is also linked to diseases of the kidneys, joints, lymph nodes, small intestine, liver and nervous system. Depression of the immune system makes infected cats more susceptible to infections. As a result, they may be infected by organisms that healthy cats usually fend off. It is possible for FeLV positive cats to remain healthy. However, the prognosis is poor for cats with persistent active infection.12

Detection of FeLV

Veterinarians use several different laboratory tests to detect FeLV. These include 1) an antigenAny substance capable of being recognized by the immune system. Recognition of such a substance leads to the generation of an immune response. enzymeA protein that speeds up the process of chemical reactions in the body without becoming altered in the process. Almost every biological process is driven by the activity of enzymes. Without enzyme catalysts, the complex reactions that build and break down cell parts would not happen at a rate compatible with life. Enzyme names usually describe the reaction that is being catalyzed and all of them end in -ase.-linked immunosorbent assay (ELISA) and 2) an indirect immunofluorescent antibodyAntibody molecules tightly bind to their targets (usually proteins) with great specificity. Antibody binding alerts the immune system to target the bound molecule for destruction. Specific antibodies can be made in the laboratory. assay (IFA). Both tests use blood samples to detect the presence of a protein that indicates FeLV infection. This protein is called p27, and is part of the structure of the virus.12 Inconclusive results may require additional testing with other methods, such as a specific type of polymerase chain reaction (PCR), which can detect FeLV DNAAbbreviation for deoxyribonucleic acid. Composed of very long strings of nucleotides, which are abbreviated as A, C, G and T. DNA is the storage form of our genetic material. All of the instructions for the production of proteins are encoded in our DNA. in infected animals.

 

Treatment for FeLV Infection

Currently there is no cure for FeLV. However there are a number of things that pet owners can do to manage FeLV positive cats, as recommended by veterinarians and experts:

  • Visit the vet every 6 months for a physical examination, complete blood count, urine analysis, and other tests
  • Carefully monitor the cat's health (i.e. measure and record weight loss)
  • Provide cat(s) with a healthy and balanced diet. Avoid uncooked meat and eggs, as well as unpasteurized dairy products to prevent food-borne infections
  • Confine cats to indoor environments to reduce exposure to harmful organisms

Antiviral therapy has been used in FeLV positive cats, but the effectiveness of the drugs is limited and they can be toxic. Medications to control and restore the immune system (immunomodulators) are also used. However data to support the proposed health benefits of these agents are limited.11, 16

Prevention of FeLV Infection

Infection with FeLV can be prevented by vaccination. The vaccine is classified as non-core, which means it can be considered optional. However both the American Association of Feline Practitioners (AAFP) and the European Advisory Board on Cat Disease (ABCD) recommend that all cats with uncertain FeLV status and/or are at risk of exposure be vaccinated. Kittens are often vaccinated at 8-9 weeks of age and again at 12 weeks of age. Research shows that the vaccine will confer immunity for up to 1 year. Many vets recommend a booster vaccination 1 year after initial vaccination and annually thereafter. Because cats become less susceptible with age, some vets consider vaccination every 2-3 years sufficient for older animals.12

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Feline Squamous Cell Carcinoma

 

Introduction


Squamous Cell Carcinoma (SCC) is a cancer that occurs in cats and dogs.  The tumors can appear many places but are seen most commonly on and around the eyes, ears, nose, mouth, and areas with little hair. 

 

Risk Factors/Detection/Staging


The primary cause of SCC is sunlight over-exposure, which is especially harmful to fair-haired cats. Age and exposure to cigarette smoke also increase the risk for SCC.17  At first, SCC tumors look much like other common skin irritations, making them difficult to identify.  Scabs, hair loss, irritated skin, loss of teeth with limited healing, and raised red bumps on the skin are all possible sign of SCC.17 Crusty sores can appear and develop into deep ulcers that bleed when irritated.  In later stages, the cancer may spread to the lymph nodes and lungs. Staging of the cancer may involve chest X-rays and testing lymph fluid.18    In advanced cases, SCC tumors can cause tissue death and destroy bone structure, leading to pain, discomfort, and possibly death.

 

Treatment


Several treatment options exist for SCC and they may be combined to increase success.  As with other cancers, the earlier SCC is detected, the more likely the treatment will be successful.  Tumors in the lower jaw or upper ear can be surgically removed.  Vets attempt to preserve as much healthy tissue as possible.  For tumors in the lower jaw, vets can perform a surgical Mandibulectomy, in which they attempt to remove the cancerous area(s).  The amount of the jaw tissue and bone removed depends on the tumor.  Possible side effects include difficulty eating and grooming, drooling, and poor appetite.17  Despite a cancer reoccurrence rate of 38% and post-operation complications, one survey revealed that over 80% of owners whose cats had surgery would choose this treatment again.17
Chemotherapy alone has not proven effective, but there is evidence that it may be effective when combined with other treatments.  A combination of the chemotherapy agent mitoXANTRONE  with external beam radiation therapy gave better results than either treatment option used alone.19   If the tumor is in the mouth, radiation should be considered with caution as it can cause severe inflammationA reaction to tissue damage or invasion. Small blood vessels become leaky, leading to redness and swelling. Cells of the immune system migrate to the area and can release chemicals and proteins that cause damage to the structures/cells nearby..  Side effects may prevent normal eating and require the use of a feeding tube. 

Cryotherapy or freeze-surgery involves insertion of a probe that freezes the tumor, killing the cancer cells.  Cryotherapy is an option for tumors under 1 cm (about 0.4 inch) in diameter.  The rate of reoccurrence is high for larger tumors.20   Cryotherapy is a good option for tumors on the upper ear because the position allows for direct and aggressive treatment. 

Photodynamic therapy (PT) is a newer treatment option for Squamous Cell Carcinoma, and is not available everywhere.  This type of treatment involves putting a light-sensitive material in the tumor and exposing the tumor to a specific wavelength of light.  This causes the light-sensitive chemical to become active and destroy the tumor cells.21   It can be used repeatedly and with other treatment options.22 The side effects include swelling, redness, sensitivity to light, and death of healthy tissue around the tumor site.  A recent study followed 12 cats with SCC that were treated with PT.  Researchers found that when used alone, PT resulted in shrinkage of shallow tumors of the nose and ear, but had little effect on deeper tumors.  When used in combination with surgery, two cats exhibited a partial response to therapy, and one exhibited a complete response.21

 

Feline Mammary Cancer

Feline Mammary Cancer Image

 

Introduction


Feline mammary cancer (FMC) is the third most common cancer in female cats.  It is very uncommon in males, but cases have been reported.23   The mammary gland tumors that result from FMC can be benignA growth that does not leave its site of origin or invade surrounding tissue. Benign growths can get large and are capable of causing illness or even death, depending on the location of the growth. Technically, benign growths are not cancer. or malignantA tumor that has invaded neighboring tissue..  However, research shows that 80-96% of mammary tumors are malignant, meaning that they can invade nearby tissues, and are capable of metastasis (spreading to distant parts of the body).23, 24  Unfortunately malignant mammary tumors tend to be much more harmful.

Cats have four mammary glands on each side of their body, any of which can be affected by FMC.  They are referred to as axillary, thoracic, abdominal, and inguinal glands.  These glands are the sites of primary tumorThe initial tumor mass formed by the abnormal growth of a cell. The primary tumor determines the type of cancer. When the initial tumor spreads to other locations, the metastatic growths retain the characteristics of the initial, primary, tumor. As an example, if the initial site of cancer development is in the breast, then a metastatic growth in the brain would still be considered breast cancer, NOT brain cancer. growth.  As with breast cancer in women, FMC is highly metastaticThe term for a cancer that has spread beyond its point of origin. Metastatic disease is responsible for the majority of cancer deaths..   As a result, this type of cancer can spread to the lungs, the lining of the lungs and chest cavity (pleura), liver, regional lymph nodes, and other parts of the body.

Genes that have been targeted in human breast cancer research have also been studied in feline mammary cancer.  HER-2/neu is the geneA stretch of DNA that leads to the production of an RNA. The RNA is produced during the process of transcription. This RNA can be used to guide the formation of a protein via translation or can be used directly in the cell. that encodes the human epidermal growth factorA substance that stimulates cell division. Growth factors are usually small proteins or steroid hormones. They may be secreted by the same cells on which they act or by cells that reside in a different part of the body than the target cells. Some examples of growth factors include estrogen, a growth factor for breast cells, and VEGF, a growth factor that causes the development of blood vessels. Several different anti-cancer treatments are designed to inhibit the activity of growth factors. receptor (type 2) protein.  This protein resides on cell surfaces, where it can interact with growth signals.  If gene amplificationAlso: gene amplification. An abnormal process in which many copies of the same chromosome region are produced via DNA replication. The result can be a small 'microsatellite' chromosome or a region of DNA within a chromosome with many contiguous copies of a small set of genes. creates extra copies of the HER-2 gene, then its corresponding protein will also be overexpressed.  This is thought to lead to increased cell proliferationRefers to cell division. The proliferation rate is an indicator of how quickly a tumor is growing. The proliferation rate may be represented as a percentage, showing what fraction of the cells are actively involved in the division process..  HER-2 overexpressionA term describing the abnormal regulation of a gene. When the controls on gene expression (transcription) break down, the gene may be turned off inappropriately, or it may be transcribed at high rates. High transcription levels lead to the production of large amounts of mRNA and large amounts of the protein product. If that protein is important in regulating cell division or some other key process, then too much protein can lead to unregulated cell division. An example is the overexpression of the Her2/neu protein on the surface of some breast and ovarian cancers. The presence of large amounts of this protein increases abnormal cell division. has been detected in up to 30% of human breast cancer cases.23   Similarly, it occurs in 30% of feline mammary cancer cases.4

 

Risk Factors/Detection/Staging


While all feline breeds may be affected by FMC, some are at a higher risk than others.4   Studies have shown the Siamese breed to have twice the risk of developing this type of cancer.23, 25   Risk increases with age up to 14 years, with an average age of tumor development between 10 and 11 years.23, 26   Early spaying reduces risk.  According to one study, intact females are 7 times more likely to develop mammary tumors than cats that are spayed at a young age.27   The latest age at which spaying  effectively reduces FMC risk has not been determined.

FMC is most often detected when pet owners or veterinarians feel a mass during examination of the mammary region.  However masses can also indicate other conditions, such as severely inflamed lesions, cysts, follicular tumors, and others.4   Histology can be used to confirm the diagnosis and classify the lesionThis is a broadly used term in pathology and refers to any defined (localized) structural abnormality or injury. The word 'lesion' does not imply that something (i.e. a tumor) is necessarily serious or advanced..  Tumors are graded as well differentiated, moderately differentiated, or poorly differentiated, based on the appearance of the tissue/cells under a microscope.

Veterinarians and researchers agree that tumor size is the most important prognostic factor in FMC cases, affecting the progression of the disease and the survival time.4   In general, larger tumors have a worse prognosis.  Lymph node involvement and degree of metastasis also determine the severity of FMC cases.

 

Treatment


Surgical removal of mammary tumors is the most common treatment choice.  This may include nodulectomy (removal of one or more cell clusters), partial or complete removal of the affected mammary gland(s), removal of lymph nodes, and mastectomy (removal of all glands on the affected side(s)).  Veterinarians may use radiation or chemotherapy in addition to surgery.  Drugs used to treat FMC include 5-fluoroucil, doxorubicin, cyclophosphamide, methotrexate, prednisone, and vincristine.28  It has been shown that cats that respond to doxorubicin-cyclophosphamide treatments survive for longer periods of time.28

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Cancer in Dogs

Cancer in Dogs

 

Dogs get a variety of cancer types. The most common is skin cancer.  Other common canine cancers include breast cancer, bone cancer, and leukemia. Other types of cancer found in dogs include cancer of the mouth, lymphoma, testicular, breast and abdominal tumors.29 Osteosarcoma, or bone cancer, is most common in large dog breeds, such as Great Danes, mastiffs, Labrador Retrievers, and Rottweilers. 3, 29 Cancers in dogs are often very similar to those in humans. Genetic risks for canine cancers can be the same as human disease.30

Canine Transmissible Venereal Tumor

Overview and Transmission

Cancer in humans is practically never transmitted from one person to another. Only very rare documented exceptions exist, usually involving surgical mishaps. Sticker's sarcomaA malignant cancer that originates in bone, muscle or connective tissues. or Canine Transmissible Venereal Tumor (CTVT) is a very unusual form of cancer affecting canines (i.e. dogs). CTVT is transmitted by mating, licking, or other direct contact.31 The tumor affects the genitalia. In some cases the urethra becomes blocked making it difficult for the affected animal to urinate.32 The image below (left) is of a CTVT tumor, showing a typical 'cauliflower-like' mounds.  The second image below (right) is a view of CTVT cancer cells as seen in a microscope.  If the cancer is located at the mouth and nose, nosebleeds, facial swelling, and nostril discharge are common symptoms.

canine transmissible veneral tumor (CTVT) Photo used courtesy of Dr. Elizabeth Murchisoncanine transmissible veneral tumor (CTVT) cytology (Wikimedia Commons)

Many human cancers are caused by viruses, including the human papilloma virus (HPV), a major cause of cervical cancer. Infection with viruses can lead to changes in normal cells within the infected person and lead to the development of cancer. CTVT is different! In this case, the cancer cells themselves are transmitted from animal to animal. Once in the new animal, the tumor can grow and eventually be spread to additional animals.33 Experiments have shown that CTVT is not transmissible via killed tumor cells or by cell contents.31 Viruses are usually present in a cell's liquid contents; if the liquid contents do not transfer CTVT, it is evidence that viruses are not responsible for the cancer. Also, all tumor cells examined so far have a molecular "fingerprint" in their DNA that is absent in normal cells. Specifically, the cancer cells contain a DNA sequence called Line-1 inserted near a known cancer-causing gene called c-mycA transcription factor that controls the expression of several genes involved in cell division. The mutant form of this gene acts as an oncogene and is associated with several types of cancer..34

Researchers have compared tumor DNA and normal DNA within different breeds of dogs. The results showed the expected differences between the normal cell DNA, but all tumor DNA samples were very similar despite being from very different dogs. These results indicate that the tumor cells themselves transfer CTVT between animals.33

The transmission of the cancer depends on physical contact between two dogs. Most of the time, the transmission of the cancer occurs during mating. It is also possible for a dog to get the cancer by sniffing a dog with the cancer. Because male dogs are more likely to sniff strange dogs, they are more likely to get the cancer in this way.35

In most cases, the immune system recognizes and eliminates cells of other types that are introduced into an animal (or human). This does not happen with CTVT. Upon the initial infection, CTVT begins a state of rapid and intense growth that lasts anywhere from three to nine months and possibly longer in old or weakened dogs.31 This is usually followed by a variable regression phase.

Treatment for CTVT

Treatment choices for CTVT include surgery, chemotherapy, or radiation therapy. Chemotherapy is often very effective, usually resulting in complete remissionA period of time in which the symptoms and signs of cancer are decreased or absent. Remission can be spontaneous or brought about by treatments. This may be of varying duration and does not necessarily indicate that a patient is cured.. Surgery does not have a similarly high success rate.36Because the cancer is transmitted between animals and across generations, the cancer itself is thought to be very old! CTVT is thought to be anywhere from 200-2500 years old and represents the longest line of unbroken replications of a mammal's body cell. Aside from domesticated dogs, it is also transmissible to coyotes, foxes, jackals, wolves and immuno-suppressed mice.31, 37

CTVT is not transmissible to humans!

 

 

Canine Osteosarcoma

Introduction

Osteosarcoma (OSA) is a cancer that develops within bones.  It is often invasive and metastatic.38   OSA is relatively rare in small domesticated animals, accounting for only 5-6% of canine malignancies.39   However, it is by far the most common primary bone tumor in dogs, accounting for 80% of cases.39, 40

Cancer in Dogs

The diagram above highlights some of the bones affected by canine osteosarcoma.   This type of cancer occurs most commonly in the appendicular skeleton, including the radius and ulna, femur, tibia, scapila, humerus, and paw bones (phalanges).  The front limbs (forelimbs) are more likely to be affected than the rear (hind) limbs.  OSA also occurs in the axial skeleton, including the spinal bones, skull, jaw bone (mandible), and the vertebrae at the base of the spine (sacrum).  In rare cases, it can affect extraskeletal tissues, such as muscle.39, 40  Because of its ability to metastasizeThe movement of a cancer to a location outside its site of origin. The distant growths are termed metastases., OSA can spread to other parts of the body.  Studies have shown that OSA invades the lungs in approximately 17% of cases.40

 

Risk Factors/Detection/Staging

Osteosarcoma is more common in adult dogs.  Large animals, weighing from 44 to 88 lbs (20 to 40 kg), are at a higher risk than smaller animals.40   

Signs of OSA in dogs include impaired movement due to pain and stiffness.  Affected dogs will often limp to avoid putting weight on the tumor-afflicted bone.  They also present with abnormal bone growth and swelling. 

Large tumor size is associated with poor prognosis.41  The location of the tumor can also affect the outcome of the disease.  Axial skeletal OSA and appendicular OSA tend to have similar prognoses.42   Tumors in the humerus bone tend to have a poor prognosis while tumors in the jaw tend to have better outcomes.41, 42

 

Treatment

Limb amputation is the standard treatment for OSA tumors located in the limbs.  Analgesics such as morphine are used to relieve pain, and most dogs can walk within 12-24 hours after the surgery.  Many dogs are able to adapt to the amputation within one month.  Interestingly, studies have shown that an owner's positive attitude can speed the adaptation process.43   Possible post-surgical complications include infection and recurrence of OSA in the stump.

Certain conditions can make dogs bad candidates for amputation, including arthritis, obesity, neurological problems and large breed.  For this reason, vets will perform limb-sparing surgeries, in which they remove the tumor and leave the surrounding tissue and bone intact.  This surgery has a higher rate of post-operation infection and OSA recurrence than amputation.  Studies reveal that the most common reason vets are asked to perform limb-sparing surgery is not based on the animals condition.  Rather, it is that owners are reluctant to proceed with amputation.44, 45

Vets can use radiation as a curative treatment or to reduce pain and make the animal more comfortable (palliative care).  This type of therapy can reduce inflammation and heal micro-fractures.  Studies show that 70% of dogs respond positively to radiation therapy and experience pain relief.39

Chemotherapy drugs such as doxorubicin, carboplatin, cisplatin, or a combination of these drugs may also be used.  Chemotherapy alone has not been shown to extend survival time.  OSA-affected dogs treated with surgery and chemotherapy tend to survive longer.46

Unfortunately, despite the treatment options available, the prognosis for canine osteosarcoma is poor.  The estimated survival time is 6 to 12 months from the time of diagnosis, regardless of the treatment used.38  The most common cause of death (or euthanasia) is disease spread (or metastasis).44

Acknowledgements: The above diagram was found using Creative Commons and can be accessed here.  It was obtained and modified on 8/10/09.

 

 

Canine Hemangiosarcoma

Cancer in Dogs

 

 

Introduction


Hemangiosarcoma (HSA) is a cancer that originates in cells that form blood vessels.  HSA is responsible for approximately 7% of canine cancer cases. In fact, it is more common in dogs than any other species of animal examined!47

HSA occurs most commonly in the spleen, skin, and the right atrium of the heart.48  Primary tumors have also been reported in the lung, aorta, kidney, oral cavity, muscle, bone, urinary bladder, prostate gland, vagina, lining of the abdominal cavity (peritoneum), intestine, tongue, and the membrane that covers the white part of the eye (conjunctiva).49, 50 HSA is highly metastatic, meaning that it frequently spreads.  When HSA is confined to the skin, it is less apt to spread.  Veterinarians estimate that over 80% of all other cases have already metastasized at the time of diagnosis.49, 50

HSA cells may release proteins that stimulate the growth of new blood vessels. This process is known as angiogenesisThe formation of blood vessels. This process is required for a tumor to grow past a small size since the blood delivers nutrients to the cells in the tumor mass., and is critical for tumor formation.  The presence of numerous blood vessels helps supply growing tumors with nutrients and oxygen and may serve as a "highway" for the cancer cells to metastasize to distant parts of the body.

 

Risk Factors


Older animals are at higher risk for developing hemangiosarcoma.  Affected dogs are usually diagnosed between 9 and 12 years of age.51  HSA tends to affect large breed animals more often than smaller ones.  Breeds that are more prone to this type of cancer include German Shepherds, Golden Retrievers, Labrador Retrievers, Pointers, Boxers, English Settlers, Great Danes, Poodles, and Siberian Huskies.  Breeds with short hair, light hair, light skin, and/or less pigmentation (i.e. Whippets) are more prone to hemangiosarcoma of the skin52, 53

 

Detection/Symptoms


Symptoms of HSA vary depending on the location and stage of the cancer, but may include weakness, weight loss, increased heart rate (tachycardia), abnormally fast breathing (tachypnea), abdominal swelling, lethargy, and paleness of mucous membranes.  Episodes of acute weakness and/or collapse may indicate that a tumor has ruptured, causing uncontrolled blood loss.  If internal bleeding occurs and the blood is reabsorbed from the body cavity back into blood vessels, the animal may gradually recover.  In more severe cases, tumor rupture can cause sudden death.50

Veterinarians often detect HSA during physical examinations.  They also use blood tests, urine analysis, chest x-rays, abdominal ultrasound, ultrasound of the heart (echocardiogram), tissue samples (biopsyA medical procedure in which a sample of tissue is removed for examination. Biopsies can range from a small sample drawn into a needle to samples taken during more invasive surgery. ), and more.  One type of blood test, the complete blood count (CBC), can detect anemia, misshapen or fragmented red blood cells, and other signs of HSA.  Some tests can even indicate the organ(s) being affected by the disease.  A blood smear that shows an increased number of immature red blood cells (normoblasts) may indicate cancer of the spleen.49, 50

 

Treatment


Surgery is the standard treatment for dogs with HSA.  In one study, researchers from Colorado State University attempted surgery on 76 animals with HSA (66 dogs and 10 cats). In 42 cases, surgeons were able to remove the tumor(s) completely, leaving no visible cancer behind.  Following surgery, all 42 of these animals remained healthy for at least 12 months.  In the remaining 34 cases, the animals experienced incomplete tumor removal and/or other complications, resulting in worse clinical outcomes.  These findings confirm that complete tumor removal is the most significant prognostic factor for this type of cancer.  Researchers also found that certain tumors (i.e. eye or skin) were much easier to remove than others (i.e. bone or muscle).54

Veterinarians can use other methods to treat and manage hemangiosarcoma, but their effectiveness is limited.  Chemotherapy can be used in addition to surgery.  Research has shown doxorubicin to be the most effective chemotherapy drug for this type of cancer.  Despite treatment, the survival time for HSA-affected dogs typically does not exceed 6 months.  Death often results from metastasis to the lungs and other parts of the body.47

 

 

Canine Mast Cell Tumors

 

Introduction


Mast cell tumors, also called mastocytomas, are the most common skin cancer in dogs.55  Mastocytomas develop most often in dogs seven and a half to nine years of age, but can occasionally be found in dogs as young as four to six months.56  Different breeds also have different rates of mast cell tumors.  Boxers and Boston terriers have the highest rates.56

Mast cell tumors originate from mast cells, immune system cells found in many tissues of the body.57   Because mast cells can be found almost anywhere, mastocytomas have the potential to appear in all different regions of the body.  They are most commonly located on the skin on hind legs, the region between the neck and abdomen (thorax), or genital regions.58    Mast cells contain a variety of biologically active substances, including histamine, heparin, serotonin, and prostaglandins.  These chemicals are released from the cells during an allergic reaction.59 These are the substances that cause the symptoms associated with allergies: redness, itching, swelling, blood pressure drops, tearing, nausea, wheezing, ect.  Normally these chemicals are highly regulated, but when mast cells become cancerous they no longer appropriately control the release of the chemicals. 

 

Risk Factors/Detection/Staging

The unregulated release of chemicals by a mastocytoma can cause a variety of symptoms.  The symptoms any particular dog shows is variable, but can include vomiting, ulcers, bloody excrement, abdominal pain, and blood-clotting difficulties; gastro-intestinal problems are the most common signs.60 Mastocytomas appear as raised lumps that are often irritated or red in appearance.  Unfortunately, mast cell tumors have no characteristic form or color and are impossible to identify without laboratory testing.55   Often when a mastocytoma is touched the skin becomes red, itchy, and swollen.56    This response is also called Darier's Sign.  It occurs because when the mast cells in the tumor are compressed they release the chemical histamine, and this causes irritation of the skin.

Although normal mast cells are typically fairly stationary, advanced mast cell tumors may spread (metastasize) to other places in the body.  Veterinarians classify (stage) mast cell tumors using a six tiered system (stages 0 to 5) based on the extent that the cancer has spread in the body.55  Staging takes into account the number and size of tumors, lymph node involvement, and recurrence rate.55  A higher stage indicates greater body involvement with Stage 5 representing distant metastasis including bone marrow or blood involvement.56  Another classification system, the histological grade (values from 1-3), is based on the physical appearance of the cells in the tumor.  More abnormal mast cells/tissues are associated with a higher histological grade and have a higher possibility of being malignant.56

 

Treatment


Surgical removal of the tumor is the most common treatment for mastocytomas of intermediate and lower stages.  Healthy tissue up to about one inch (2-3 centimeters) around the tumor must also be removed to prevent leaving any cancerous mast cells behind. For more advanced stages surgery is still recommended, but is often combined with radiation therapy or chemotherapy.56   If surgery is not thorough enough to remove all cells, external beam radiation therapy can be used to kill the remaining cells.  External beam radiation may also be used to reduce the size of a tumor before surgery.56

Cancer in Reptiles

A leopard gecko.

'Lemon Frost' Gecko

The leopard gecko is reptile. They are one of the more common reptiles to be kept as pets.

A rare type of gecko - a variety known as 'Lemon Frost' (LF), has been shown to spontaneously develop skin cancers that share a defect in common with some human melanomas. The LF gecko has been found to have defects in a gene called SPINT1. The gene is a known tumor suppressorA gene that functions in the control of cell division. Tumor suppressors normally work to limit cell division and may be contrasted with oncogenes.. It encodes a protein that is a serine peptidase inhibitor.61, 62

In the gecko, the result of defective SPINT1 genes is the development of skin cancer.63, 64, 65 The cells affected are involved in the production of skin pigments. In humans, defects in the comparable gene is linked to cancers of pigment producing cells in the skin.

Researchers are now using the LF gecko as a model to help understand the human cancers.

Learn more about tumor suppressors.

 

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