Thyroid tumors account for 1.2 % to 3.8 % of all tumors in the dog and typically develop in older dogs with a median age of 9-11 years. There is no gender predisposition but Golden retrievers, Boxers, and Beagles are over represented. Most thyroid carcinomas are non-functional (meaning they don’t produce thyroid hormones); 60% of patients have normal thyroid function; 30% are hypothyroid (under active thyroid); 10% are hyperthyroid (over active thyroid). Approximately 30-40% of thyroid carcinomas will have already metastasized (spread) at the time of diagnosis and ~80% will ultimately develop metastasis.

Thymomas are rare tumors that arise from the epithelium (lining) of the thymus gland in the dog and cat. They are typically diagnosed in older animals, with the median age in dogs being 9 years and in cats it is 10 years. There is no breed predilection but medium and large dogs are overrepresented. Thymomas are considered benign or malignant based on their clinical features rather than on histologic (under the microscope) features. Benign thymomas do not invade into adjacent structures within the chest cavity while malignant thymomas do invade adjacent structures

Soft tissue sarcomas (STS) make up a large category of tumors that arise from connective tissue. This category includes tumors of fibrous tissue, fat, smooth muscle, nerves, and lymphatic vessels. The diagnosis of soft tissue sarcoma includes fibrosarcomas, malignant peripheral nerve sheath tumors, histiocytomas, myxosarcomas, liposarcomas, lymphangiosarcomas, and undifferentiated sarcomas. STS comprise ~15% of all skin/subcutaneous (under the skin) tumors. These tumors are typically very invasive to the surrounding tissue but generally have a low risk of spreading (metastasis).

Primary lung tumors (cancer originating in the lung) are uncommon in dogs and account for less than 1% of all tumors. It is most common in older dogs, but no specific breed or sex is predisposed. They are almost always malignant (invasive with the potential to spread).

Multiple Myeloma (MM) is a cancer of plasma cells, which are specific types of B-lymphocytes (white blood cells) which produce antibodies as part of the body’s immune system. Multiple Myeloma is a relatively uncommon cancer and there is no gender or breed predilection in dogs. The average age at the time of diagnosis is 8-9 years

Melanoma is the most common tumor found in the mouth of dogs, and the second most common tumor found is on the digits (toes). There is a predisposition for male dogs and certain breeds seem to be overepresented, including Scottish terriers, Cocker Spaniels, Gordon Setters, Chow Chows, and Golden retrievers.  They are locally invasive tumors, often infiltrate deep into the bone (of the jaw or toe), and have a high rate of metastasis (spreading). Cats can also get melanomas but it is much less common than in the dog.

The most common tumor of the spleen in dogs is hemangiosarcoma (HSA). Up to 50% of dogs with splenic HSA are in DIC (disseminated intravascular coagulation, or inability to clot blood) at the time of presentation. Unfortunately, with surgery alone, the average survival times are only around 3 months. Liver biopsy is essential to differentiate between liver metastasis (spread) and benign hyperplasia (increased tissue growth).  HSA does not always start in the liver or spleen; it can also start in the skin, subcutaneous tissue, or the heart. Stage I cutaneous HSA may be cured with aggressive surgical resection. Radiographs (x-rays) of the lungs are required to rule out pulmonary metastasis (tumors in the lungs). Cardiac HSA is a common cause of pericardial effusion (fluid surrounding the heart) in dogs. HSA in cats is rare but occurs most commonly within the abdomen (spleen, liver or kidneys) or subcutaneous tissue (under the skin)

Chronic Lymphocytic leukemia (CLL) is a condition in which mature (i.e., “normal”-looking) lymphocytes (a type of white blood cell) accumulate in the body (including in the bone marrow and spleen). This results in elevated circulating lymphocyte counts on CBC blood tests. CLL typically occurs in middle age to older dogs and is often found “accidentally” when blood work is being performed for other reasons. CLL usually progresses slowly and patients can typically be medically managed and live well for years.

Urinary bladder cancers are more common in female dogs, with Scottish Terriers, West Highland White Terriers, Shetland Sheepdogs, and Beagles being overrepresented. Transitional cell carcinoma (TCC) is by far the most common type of bladder neoplasia (cancer) encountered in dogs.

Mast cell tumors (MCT) are the most common malignant skin tumors in dogs and among the most common tumors overall. MCT most commonly occur as solitary lumps or masses in the skin and occasionally dogs can have multiple MCTs. These tumors can have a very variable appearance–they can resemble fatty (lipomatous) masses or may be reddened (erythematous) and/or ulcerated. MCT may change quickly, often waxing and waning in size  (become larger, then smaller). They do this because mast cells contain granules of histamine, heparin and other chemicals that when released into the body can cause swelling, redness, and increased stomach acid production.

Mammary tumors (breast cancers) are the most commonly diagnosed tumor in intact female dogs older than 7 years of age. Male dogs can also develop mammary tumors, but rarely. Several breeds are prone to developing mammary cancer including Poodles, English Spaniels, English Setters, and Terriers. About 50% of mammary tumors are malignant (invasive to surrounding tissue with a high risk of spreading) and 50% are benign—this is very similar to the statistics for breast cancer in women.

Lymphoma and lymphosarcoma (LSA) are interchangeable terms. Lymphoma in dogs is very similar to non-Hodgkin’s lymphoma in people. Lymphoma represents 7% of all cancers in dogs. Most affected dogs are between 5-9 years of age, but the disease can occur in dogs of any age. Generalized lymphadenopathy (lymph node enlargement) in an otherwise healthy dog is the most common presentation. Hypercalcemia (high blood calcium) occurs in 20% of dogs with lymphoma. Administration of glucocorticoids (steroids) prior to confirming a diagnosis can make obtaining the diagnosis much more difficult and lead to the cancer becoming chemotherapy resistant.

Appendicular osteosarcoma (bone cancer of the leg) is most common in giant and large breed dogs, with an average age of onset of 7 years. The most common site for the development of osteosarcoma (OSA) is the distal radius (near the wrist), followed by the proximal humerus (near the shoulder) and less commonly proximal and distal femur and tibia (hips to ankles). While acute lameness due to pathologic fracture (disease-related bone break) occurs in some dogs, most present with a history of progressive lameness over several weeks.

Acute leukemia is a systemic cancer characterized by the infiltration of immature lymphocytes or myelocytes (two types of white blood cells) called in the bone marrow (and commonly in the liver and spleen as well). Patients with acute leukemia are typically quite ill due to their disease. Affected animals are typically young (less than 5 years of age). There is a male gender predilection in some studies.

Vaccine-associated fibrosarcomas (VAS) are tumors of connective tissue that develop at sites of previous vaccinations. Vaccine associated fibrosarcomas (VAS) are thought to develop in 1/1000 to 1/10,000 cases. The time it takes for a tumor to develop after a vaccine can be anywhere from 4 months to over 10 years. These tumors typically behave in a very aggressive fashion. These tumors can extend up to 5 cm beyond the margins of the tumor and there is evidence of metastasis (disease that has spread) at diagnosis in approximately 12% of the cases.  These tumors invade through tissue planes sending out projections of tumor cells much like the roots of a tree. Due to this fact, complete surgical excision can be difficult and the mass that is visible on the skin is usually only the “tip of the iceberg” as there can be a significant amount of disease below the surface. VAS are more locally aggressive (30-70% recurrence rates) and systemically aggressive (~25% metastatic rate) than fibrosarcomas that are not caused by vaccinations.

Adenocarcinomas are one of the three most common tumors that arise in the gastrointestinal tract (stomach, duodenum, jejunum, ileum, and colon) of cats–the other two being lymphoma and mast cell tumors. These tumors typically occur in older cats and there is a male predilection. Both Siamese cats and Domestic Shorthair cats have been reported to have a higher incidence of this disease.

Squamous cell carcinoma (SCC) is the most common oral tumor in cats. They can be extremely invasive (invading the bone of the jaw) but do not tend to metastasize (spread to other areas of the body) very rapidly.

Mast cells are a type of normal white blood cell and are part of the immune system.  Mast cell tumors (MCT) comprise about 20% of all cutaneous (skin) tumors in the cat. These tumors can be benign (not cancerous) or malignant (cancerous and able to spread to other parts of the body). Over 90% of MCTs that occur in the skin of cats are benign while visceral (occurring in internal organs) MCTs may behave more aggressively.  This disease is seen mostly in middle-aged cats, and Siamese cats appear to be predisposed to getting this disease.

Mammary tumors are the third most common tumor type seen in the cat, and they account for approximately 20% of cancer in the female cat. These tumors arise from the mammary (breast) tissue and are typically malignant (invasive with a high chance of spreading). Most mammary tumors in cats are classified as adenocarcinomas. About 85% of mammary tumors in cats are malignant; meaning they are very invasive to the surrounding tissues and have a high rate of spreading to other areas of the body. Mammary cancer is often a disease of middle aged to older cats, with Siamese cats having a higher risk.

Lymphoma accounts for one-third of all malignancies in cats and occurs in various primary anatomic sites, such as the gastrointestinal tract, kidneys, mediastinum (chest cavity) and spleen. Unlike in dogs with lymphoma, cats generally do not present with generalized peripheral lymph node enlargement.The occurrence of feline lymphoma has been strongly associated with infection by the feline leukemia virus (FeLV) and certain strains of the feline immunodeficiency virus (FIV) although over the last 10 years, the use of testing and vaccination has dramatically reduced the incidence of FeLV infection in the United States. A combination of 5 chemotherapy drugs is reported to be the most effective method to treat most types of lymphoma in cats. Radiation therapy and surgery, along with chemotherapy, are used to treat the more localized forms of lymphoma (such as intra-nasal or ocular.) Treatment goals are to improve quality of life by achieving remission with minimal toxicity and side effects from the drugs.

Acute leukemia is a systemic cancer characterized by the infiltration of immature lymphocytes or myelocytes (two types of white blood cells) found in the bone marrow (and commonly in the liver and spleen as well). Patients with acute leukemia are typically quite ill due to their disease. Affected animals are typically young (less than 5 years of age). There is a male gender predilection in some studies.