Common feline cancers (Proceedings)

Lymphoma

Lymphoma (LSA) is one of the most common feline malignancies, comprising approximately 30% of all reported tumors. While not curable, LSA may respond quite well to therapy and can be a very satisfying neoplasm to treat.

Signalment

The age of cats affected has increased over the past 10 years, due to the decline in FeLV+ cases. Middle-aged to older cats are mainly affected. Young cats with LSA are often FeLV+.

Etiology

FeLV is linked with most forms of LSA except the GI form. FeLV+ LSA is a T cell variant and occurs in younger cats (2 to 4 years). The risk of developing LSA is increased by 5x with FIV infection and by 77x with FeLV and FIV co-infection. FeLV can directly cause malignant transformation, while FIV is thought to predispose to lymphoma via immune dysfunction. Inflammatory bowel disease may ultimately progress to lymphoma, but this theory is not proven.

History

Presenting complaints in cats depends on the form of LSA affecting the patient. As the GI form is the most common, signs include any or all of the following: weight loss, inappetance, lethargy, vomiting, and/or diarrhea. Multicentric cases will usually be ill and have enlarged lymph nodes ("lumps" noted by owner). Mediastinal LSA causes dyspnea (from the mass or secondary pleural effusion) and/or regurgitation (also a mass effect). Extranodal LSA also will present with concerns based on location: sneezing/epistaxis for nasal, paresis/paralysis for CNS, systemic illness with the renal form, and blindness or discomfort in ocular cases.

Diagnostic evaluation/staging

Depending on the form of the cancer, the diagnosis of LSA in cats may be achieved with fine needle aspirate (FNA) or may require histopathology. Situations where biopsies are indicated include the GI form that is microscopic and diffuse, multicentric lymphoma (peripheral lymph nodes can be enlarged for a number of non-neoplastic causes which may not be cytologically distinguishable), nasal and cutaneous LSA.

As LSA is almost always a systemic disease, staging to determine extent of disease is important for prognosis and monitoring response to therapy. Many of the specific forms of LSA do not stay isolated to the primary location. For example, renal LSA may progress to involve the CNS, and spinal LSA frequently involves the bone marrow. However, staging may not be indicated in cats that have a very poor prognosis at diagnosis (eg FeLV+ mediastinal LSA, leukemia).

Diagnostic evaluation of cats with LSA includes a complete blood count, serum chemistry profile, urinalysis, FeLV/FIV testing, bone marrow aspirate, thoracic and abdominal radiographs and abdominal ultrasound. Clinical substage is based on symptoms: substage a is asymptomatic, substage b correlates with an ill patient.

Prognostic factors

Unlike in dogs, there are not many prognostic factors in cats that help to predict which cats will respond to therapy. The anatomic location of the lymphoma may be prognostic; some forms may respond better than others. Such information is somewhat unclear due to most studies grouping together cats with various forms in the remission/survival analysis, and due to small numbers of cats in the studies. Other prognostic factors include clinical substage (b does worse) and FeLV status (+ have decreased remission times). One of the most prognostic findings, which unfortunately cannot be assessed prior to treatment, is response to therapy (cats that go into remission have greatly prolonged survivals).

Treatment/Prognosis

Overall, cats tolerate chemotherapy extremely well. The most common side effect is anorexia (~20%), but even that is usually not severe and is short lasting. Neutropenia may occur, but is fairly rare with the chemotherapy used for lymphoma. Cats will lose their whiskers and their guard hairs – leading to a soft, fluffy coat. Constipation may be seen, particularly with vincristine. Renal function needs to be monitored with doxorubicin administration, but cumulative doses up to 150 mg/m2 are generally well-tolerated. Protocols containing doxorubicin lead to increased remission rates and survival times in cats with LSA over non-doxorubicin protocols. Other options include single agent doxorubicin or a COP (cyclophosphamide, vincristine, prednisone) protocol. Overall, remission rates range between 50-70%, with survivals around 6-12 months. However, some cats will have survival times >2 years. The following is a brief summary of different sites and prognoses.

Multicentric

FeLV - cats with disease on one side of the diaphragm (median survival 171/2 mos) do better than FeLV+ cats or cats with disease on both sides (median survival 3 months).

GI

Roughly 1/3 of cases respond to treatment, these cats live a median of 1 year. 20-40% of the responders may have survivals >3-5 years.

Nasal

Very good prognosis – this disease is usually confined to the nasal cavity and can do excellently with local radiation, with median survival approx 1.5 years. If radiation not available, may respond to chemotherapy.

Mediastinal

Usually FeLV+, survival median 2-4 months.

CNS

Few reported cases, but overall poor survivals. To diagnose, 35% of cats had lymphoblasts in CSF. Close to 80% have bone marrow or renal involvement – testing these areas first in a paretic cat is a quicker and easier procedure. Chemotherapy is necessary, may need local treatment (surgery/radiation) also.

Renal

Median survival 3-6 months. Renal failure not a prognostic factor. 40% developed CNS involvement.

Ocular

May be associated with systemic disease, but does occur as a primary, extra nodal site. These primary cases can have prolonged survivals with enucleation alone. Make sure to fully stage these cats in case there is systemic disease. FeLV+ and uveitis were poor prognostic factors. Median survival was not reached at 450 days of follow-up if FeLV- and no uveitis. With uveitis, 250 day median survival.

Mast cell tumors

Mast cell tumors (MCT) are the second most common cutaneous tumor in cats and comprise 20% of reported skin tumors. Older cats are affected (average of 9 years), any breed, no sex predilection. There are 3 distinct forms of MCT in cats:

          • Cutaneous (very rarely subQ) MCT occurs most commonly on the head & neck.

          • Splenic form, PE reveals massive splenomegaly, usually diffusely enlarged but sometimes nodular. Abdominal effusion may be noted. Cats present ill.

          • GI form, an intraabdominal mass is palpated - may be solitary or multiple. Vomiting is common sign. Again, cats present ill.

Biologic Behavior

The three forms have three distinct biologic behaviors

          • Cutaneous - Less locally invasive than canine cutaneous MCT. Not associated with visceral disease. Staging tests unnecessary. Almost always benign.

          • Splenic - Circulating mastocytosis and liver involvement is often observed with this form of disease, but treatment (see below) can resolve this for some time. Systemic involvement will recur.

          • GI - While it may be one mass grossly, often infiltrative microscopically throughout the intestinal tract. May involve mesenteric LNs.

Treatment/Prognosis

          • Cutaneous - Surgical excision usually curative. Narrow (0.5-1 cm) margins are usually adequate. If in a bad location (e.g. eyelid) plesiotherapy (local radiation therapy with a strontium probe) can be effective.

          • Splenic - Splenectomy alone will provide good remission times (12 to 19 months). Monitor buffy coat smear for increasing mast cell counts as an indicator of failing remission. Chemotherapy may be of benefit at that time. Vinblastine 2mg/m2 weekly x 4, then every other week x4; or lomustine 60mg/m2 PO q 4-6 weeks.

          • GI - Poorly responsive to surgery or chemotherapy. If solitary mass, may try to excise with wide margins and follow with chemotherapy. Rare cats may benefit with treatment, even so, survival times usually < 1yr.

Basal cell tumors

The most common skin tumor in cats, almost always benign and easily excisable.

Vaccine associated sarcomas

Common? Well, too common for us! VAS have been associated with adjuvanted (killed) vaccines, namely FeLV and Rabies. Typical location is at vaccine sites: interscapular and hind leg. Tumors may develop years (7 years has been noted) after the last vaccination (average time in one prospective study was 26 months). In the years post 1996, a shift in location has been reported, with an increased number of tumors developing in the hind legs (consistent with new vaccination recommendations) vs the thoracic region. Unfortunately, an increase in tumors on the lateral abdomen was also noted – this finding was thought to be likely due to misplaced attempts to vaccinate over the stifle. Additionally, tumors were still noted frequently in the interscapular region, thus showing that new vaccine recommendations are not followed by many veterinarians.

Biologic behavior

Very locally invasive, with a metastatic rate higher than most soft tissue sarcomas: up to 25%.

Treatment/prognosis

Wide (3-5 cm margins) surgical excision is necessary, yet rarely possible due to tumor location. Aggressive surgery at diagnosis will extend survival times. Radiation therapy and chemotherapy may also play roles, yet will not be curative. Even with multimodality therapy, survival times range from only 600-700 days.

Prevention

Do not over-vaccinate, and use the hind legs near the stifle, so amputation may be performed if needed.