Specific Types of Neoplasia in Dogs and Cats

As mentioned previously in this site, countless types of neoplasms can arise in dogs and cats; however, certain types appear more frequently than others.

Adenomas are tumors affecting glandular structures within the body. Adenomas arising from the sebaceous glands of the skin account for the largest percentage of tumors affecting dogs. There is no sex predilection for these tumors, and most occur in animals over 9 years of age. Sebaceous gland adenomas are cauliflower, wartlike growths and are pink to orange in appearance, although some may be pigmented. Sites most commonly affected include the limbs, trunk, eyelids, and head. In most cases, they are benign in character and pose little threat to the health of the pet.

Diagnosis of sebaceous gland adenomas is based on physical appearance and biopsy test results. Treatment consists of surgical excision, cryotherapy, and/or heat therapy. Once removed, they rarely recur in the same location. However, they may appear elsewhere on the body. In those instances in which multiple adenomas exist on a particular pet, treatment is sometimes bypassed altogether, unless the tumors appear to be growing extraordinarily fast or become ulcerated or traumatized.

Adenomas can also arise from modified skin glands in the region of the anus (perianal glands) and anal sacs of dogs. Seen most often in dogs over 11 years of age, perianal gland adenomas are nine times more likely to occur in male dogs than in females. The reason for this is that the activities of these glands are normally modulated by sex hormones, mainly the male hormone testosterone. Interestingly, female dogs afflicted with Cushing’s disease may be predisposed to these tumors because disease-induced elevated levels of testosterone are produced by the adrenal glands.

Most tumors involving the perianal glands are benign in nature; however, malignancy (adenocarcinoma) can occur, especially if the tumor involves the anal sac. As a result, diagnosis of these tumors should always include biopsy evaluation to determine their status. The treatment of choice for benign adenomas is castration to remove the source of hormonal influence. In addition, in extensive cases, surgical excision, chemotherapy, and even radiation therapy can be used to attempt a cure. Therapy with estrogen compounds is often used to treat malignant adenomas and also female dogs that may be afflicted with benign or malignant tumors. Prognosis for recovery is good to excellent with benign tumors, but guarded to poor with malignancies.

Cats can be affected with several different types of adenomas as well. Two of the more common forms of adenomas and adenocarcinomas seen in cats include ceruminous gland tumors, which affect the ears and ear canals, and thyroid adenomas, which are responsible for the development of hyperthyroidism.

Tumors involving the mammary glands, including mammary adenocarcinomas, are quite common among both canines and felines. Owing to the hormonal influences on mammary tissue, female dogs and cats are more likely to develop such tumors than are males. These neoplasms can arise from a number of cell types within the mammary tissue itself, and can be benign or malignant in nature. Malignant mammary neoplasms grow quite rapidly, and tend to invade and cause inflammation in and around surrounding tissue. Metastasis to other organs such as the lungs, liver, bone, and kidney can occur as well. Mammary tumors appear as hardened, sometimes painful swellings usually involving the last two glands of the mammary chain, although the others may also be affected. Local lymph node enlargement, especially in the groin region, may become noticeable as well. A fluid discharge from the affected nipples may occur, and, if metastasis takes place, breathing difficulties, coughing, swollen limbs, vomiting, and/or diarrhea may arise.

The treatment of choice for any type of mammary tumor is surgical excision. This may involve simply removing the mass if only one location along the mammary chain is affected, or in the case of multiple locations, the entire gland or a large portion thereof may need to be removed. Since mammary tumors are usually highly malignant in cats, radical mastectomies are indicated in all cases. Regional lymph nodes are removed as well if metastasis is suspected. On biopsy of the affected tissue, subsequent chemotherapy is recommended if the tumor is deemed malignant.

It should be noted that female dogs that are spayed prior to their first heat cycle experience a dramatically reduced incidence of mammary cancer when compared to those females that were allowed to go through one or more heat cycles. As a result, this is a great way to prevent this devastating form of cancer.

Lipomas are relatively common tumors in dogs that can arise from fatty tissue anywhere in the body. Dachshunds, cocker spaniels, poodles, and terriers seem to be especially predisposed to this type of tumor. The most prevalent sites of occurrence include the subdermal (beneath the skin) fatty tissue on the belly and chest regions. Lipomas present as soft, fluctuant round masses that are adhered tightly to surrounding tissue. As a rule, lipomas rarely pose a health risk to a dog, unless they become secondarily infected or achieve such a size as to mechanically interfere with normal body functions. This can occur within the body cavities, where lipomas arising from fat adhere to body organs or from membranes lining the cavities form large space-occupying masses that can impinge on surrounding organs.

Surgical removal is the treatment of choice for lipomas, yet they can sometimes be difficult to completely excise because they tend to infiltrate into surrounding muscles and tissues. As a result, recurrences following surgery are not uncommon. In many instances, if tumor growth is minimal and there is little to no interference with normal body function, lipomas are left untreated.

The malignant form of fatty tumors, liposarcomas, are rare in dogs, yet must be ruled out whenever a fatty mass is discovered. Veterinarians can distinguish lipomas from liposarcomas through cytology and biopsy procedures. If a malignancy is diagnosed, liberal surgical excision of the mass and a portion of the surrounding tissue is indicated in an effort to completely remove the cancer. Chemotherapy is indicated as well.

Another prevalent form of neoplasia in cats and dogs is malignant lymphoma-lymphosarcoma (LSA). In fact, this is by far the most common form of neoplasia found in cats. This type of cancer involves the neoplastic proliferation of lymphocytes in sites throughout the body, including the lymph nodes, digestive tract, skin, spleen, liver, and kidneys.

In dogs, the primary clinical sign associated with malignant lymphoma typically includes a generalized swelling of the lymph nodes throughout the body, especially noticeable on the neck, shoulder, hindlimb, and inguinal regions. Other nonspecific signs may appear as organ systems within the body are adversely affected.

In cats, lymphosarcoma is usually seen concurrently with FeLV infections. There are a number of different presentations or forms of this particular neoplastic condition in felines. Alimentary lymphosarcoma affects primarily the intestines and associated lymphatic tissue. Other organs within the abdomen can be affected as well. Symptoms commonly seen with alimentary lymphosarcoma include loss of appetite, weight loss, vomiting, diarrhea, bloody stool, jaundice, and/or constipation. The mediastinal form of lymphosarcoma presents itself as the proliferation of a large tumor within the chest cavity. As one might expect, prominent signs seen with this form include breathing difficulties, coughing, pleural effusions, chest wall incompressibility, and swallowing difficulties. Multicentric lymphosarcoma affects lymph nodes and tissue in multiple sites throughout the body, all at one time. The signs seen with this type are variable, depending on the organs most heavily involved. Prominent swelling of the lymph nodes, including those situated beneath the skin, is usually seen with this form of LSA. Atypical lymphosarcoma is a form of lymphosarcoma that is limited to solitary organs or organ systems within the body. Such solitary sites may include the skin, eyes, spinal cord, muscles, brain, and kidneys. Obviously, symptoms exhibited will reflect the organ(s) involved. Finally, lymphocytic leukemia is a type of lymphosarcoma characterized by the growth and proliferation of neoplastic lymphocytes within the blood and bone marrow, often affecting secondary structures such as the spleen and liver. Symptoms associated with lymphocytic leukemia tend to be nonspecific in nature, and can include anemia, jaundice, loss of appetite, weakness, fever, and organomegally (enlargement of internal organs).

Diagnosis of malignant lymphoma in dogs and cats can be achieved through lymph node cytology and biopsy, radiographs of the abdomen and chest, and ultrasonography of the same. FeLV testing of affected cats will often yield positive results, although not always.

Treatment for malignant lymphoma for both dogs and cats involves chemotherapy, radiation therapy, and in select cases, immunotherapy. Unfortunately, the prognosis for a long-term remission (extending beyond 6 months) is poor for most patients.

Myeloproliferative disorders and leukemia are a family of disorders seen primarily in cats and characterized by a neoplastic proliferation of the cellular components of the bone marrow, including the white blood cells, red blood cells, and platelets. Again, the feline leukemia virus is the culprit responsible for most myeloproliferative disorders seen in cats. Symptoms associated with these disorders are often related to anemia and blood clotting disorders (weakness, labored breathing, pale mucous membranes, loss of appetite), as the proliferating cells, especially white blood cells, within the bone marrow interfere with the normal production of red blood cells and platelets. In addition, certain myeloproliferative disorders are characterized by the abnormal production of the red blood cells and platelets themselves, leading again to those signs mentioned previously, and also to an enlargement of the spleen and liver. Definitive diagnosis of a myeloproliferative disorder or leukemia is made on evaluation of the blood and a biopsy sample of the bone marrow. Chemotherapy is the treatment approach of choice. Bone marrow transplants, although not readily performed on cats, can be useful as well.

Melanomas are neoplasms seen most often affecting the integument of dogs, with a special predilection for the lips, tongue, gums, oral cavity, eyelids, and the digits of the feet. Arising from pigment-producing epithelial cells, melanomas may be either benign or malignant in nature. In fact, the degree of malignancy exhibited by these tumors seems to be directly correlated with where they are located. For example, melanomas involving the mouth and oral cavity tend to be more malignant than those affecting the digits or eyelids. Male dogs seem to have a higher occurrence of this type of skin tumor than do females.

Benign melanomas appear as darkly pigmented nodules or skin blotches with well-defined borders. Rarely do they exceed 1 inch in diameter. Malignant melanomas, on the other hand, appear as rapidly growing, often ulcerated masses or nodules that may or may not be pigmented and can reach greater sizes. These cancers often metastasize via the blood and lymph to various organs throughout the body, including the liver, lungs, spleen, brain, spinal cord, heart, and bone. As with other tumors, definitive diagnosis of a melanoma and whether a malignancy exists is accomplished through biopsy and microscopic examination of the tumor. Radiography, ultrasonography, and lymph node biopsies may all be used to help determine the extent of metastasis if a malignancy is diagnosed. Treatment involves the surgical removal of the tumor and radiation therapy. Chemotherapy has proved to be of limited use in the treatment of malignant melanoma. Unfortunately, malignant melanomas have usually undergone metastasis by the time they are first recognized, and tend to recur after surgical removal. As a result, an overall prognosis for cure is poor.

Although melanomas are not common in cats, basal cell tumors are. In fact, these are the most prevalent skin tumors seen in cats. These tumors, which are usually benign in nature, present as a firm, raised nodule with or without an ulcerated surface. They may also be heavily pigmented, appearing brown to black in color. Basal cell tumors originate from the deeper layers of the skin, hair follicles, and/or sebaceous glands. Sites most often affected include the skin of the head, neck, ears, and shoulder regions. These tumors can usually be treated quite successfully with surgical removal of the tumor, chemotherapy, and/or radiation therapy.

Still another type of neoplasia that can arise from the skin epithelial cells of dogs and cats are squamous cell carcinomas (SCCs). Areas of skin lacking pigment or subject to repeated trauma or irritation are especially susceptible to squamous cell carcinoma development. The oral cavity, tonsils, lips, nose, eyelids, external ear, and limbs are common sites of occurrence. squamous cell carcinoma can involve the nails and toes as well.

A squamous cell carcinoma may appear as a slightly raised mass, often with an ulcerated surface, or it may actually resemble a papule or wart. As a rule, these tumors are slow to spread to other organs, yet usually readily invade surrounding tissue. Diagnosis is achieved through biopsy evaluation of the actual tumor. Surgery, cryotherapy, hyperthermia, chemotherapy, and radiation therapy are the most effective ways to treat squamous cell carcinoma in dogs and cats.

Mast cell tumors (mastocytoma) may present as solitary or multiple skin nodules, some of which may be ulcerated and pigmented. Seen primarily in dogs, such tumors may be located anywhere on the body, yet those located around the reproductive structures and on the digits of the feet seem to exhibit a higher degree of malignancy than do those in other locations.

Mast cell tumors are especially significant because the cells making up the tumor are filled with granules containing histamine and several other powerful chemicals that can have profound effects on the body if released from the cells. Some of these effects include gastrointestinal ulcers, interference with normal blood clotting, and kidney inflammation. Diagnosis of a mast cell tumor can often be made on cytological examination and biopsy of a tumor sample. In addition, evaluation of the blood often reveals abnormalities related to the release of histamine and other granules, such as low platelet counts, anemia, and elevations in white blood cells.

Treatment for mast cell tumors employs a wide variety of techniques because of the stubborn nature of this neoplasia. Surgical excision of the visible mass along with a generous portion of healthy tissue surrounding the mass (to ensure complete removal) is usually the first step taken. Veterinary surgeons must exercise extreme care when handling these tumors, since excessive handling could cause a massive release of granules from the tumor that can induce shock and collapse. Following surgical recovery, radiation therapy and chemotherapy may be employed to help reduce the chances of recurrence and metastatic growth. Cryotherapy is also employed in those instances in which surgical excision of the tumor is incomplete or impossible.

Osteosarcoma (OSA) is a highly malignant tumor involving the bones and joints. This tumor is quite destructive in nature and metastasizes readily to other organs of the body, especially the lungs. Locally, bone destruction with infiltration of surrounding tissues occurs in most cases. The most common site of involvement in dogs is the forearm, yet the tumor can also appear on the hindlimbs and even facial bones. In cats, the hindlimbs and skull are the areas most often affected.

Clinical signs associated with osteosarcoma include limb swelling and lameness. Coughing, breathing difficulties, and other signs related to internal organ involvement may also be seen if metastasis has occurred. Diagnosis can usually be made with clinical signs and with radiographs of the affected bones. Of course, biopsy evaluation is needed to confirm such a diagnosis.

Treatment for an osteosarcoma invading the bone of a limb involves aggressive surgical intervention, including amputation of the affected limb or special surgical techniques designed to preserve limb integrity while allowing for tumor removal. Chemotherapy should follow surgery to slow or eliminate metastatic disease. If chemotherapy is not instituted, most pets diagnosed with osteosarcoma and treated with surgery alone will die within 1 year following diagnosis.

Fibrosarcomas are malignant tumors arising from the fibrous tissue located just beneath the skin. They usually present as solitary, irregular masses on or protruding from the skin. Their surfaces may or may not be ulcerated. In addition, fibrosarcomas have been known to develop at sites of vaccine administration along the back and flank regions of cats. When they occur, fibrosarcomas aggressively invade local tissue, and secondary metastasis to the lungs and lymph nodes is not uncommon.

Diagnosis of fibrosarcomas is made through biopsy evaluation. Treatment usually involves a combination of surgery, radiation therapy, and chemotherapy; surgery is the most important of the three.

Hemangiomas and hemangiosarcomas are neoplasms seen primarily in dogs that arise from the cells within the blood vessels. Common sites of occurrence include the spleen, heart, liver, and skin, although any organ within the body can be affected if metastasis via the blood takes place. Hemangiosarcomas tend to be very malignant and often ulcerate as a result of rapid growth. German shepherds, boxers, Scottish terriers, and Airedale terriers seem to have the highest incidence of this tumor type.

Clinical signs associated with hemangiomas and hemangiosarcomas involving the skin include the appearance of soft, friable masses, usually on the chest or extremities. If the spleen or other internal organs are involved, symptoms seen include weakness and depression, abdominal swelling, breathing difficulties, progressive emaciation, enlarged lymph nodes, and/or nosebleeds. Overt collapse and shock can occur secondary to excessive bleeding typically from the spleen.

Diagnosis of these blood vessel tumors is based on clinical signs and tumor biopsy results. Surgical excision or cryotherapy can be utilized on hemangiomas with favorable results. Hemangiosarcomas, on the other hand, provide a greater treatment challenge because of their invasive and metastatic nature. Often, amputation of an entire limb may be required because of the tumor’s invasiveness. Removal of the spleen is indicated in cases of splenic hemangiosarcoma. Chemotherapy can be employed postsurgically, yet the prognosis for a lasting recovery still remains poor.

Bladder tumors are relatively common in dogs. They can arise from a variety of different tissues that constitute this organ. The two most prevalent bladder neoplasms include transitional cell carcinomas and squamous cell carcinomas. Female dogs seem to be affected more than males.

Tumors present within the urinary bladder can predispose to secondary infection and urolith formation. In instances where the tumor is especially large, it can obstruct the outflow of urine and cause associated complications. Clinical signs of a bladder tumor include bloody urine, straining to urinate, and painful urinations. Diagnosis is achieved through an evaluation of the urine as well as contrast radiographs or ultrasonography of the bladder. Biochemical evaluation of the blood may reveal elevated kidney enzymes if the kidneys have been damaged by an obstruction to urine flow.

Benign and malignant bladder tumors are best treated by surgical excision if their location and involvement permit. Unfortunately, most malignant bladder tumors are highly metastatic; as a result, the chances of recurrence after surgery are high. For this reason, both chemotherapy and radiation therapy may be employed after surgery to help reduce the chances of this recurrence and to attack any spread that may have taken place.