Lymphoma

Lymphoma is the most common malignancy in cats. Classification is by anatomic location and cell size.

Anatomic forms (incidence):

• Alimentary (GI): Most common (~50–70%); older cats; small cell or large cell
• Mediastinal: Young cats (< 3 years); often FeLV-positive; dyspnea, pleural effusion
• Renal: Bilateral renomegaly, azotemia, PU/PD
• Nasal: Chronic nasal discharge, facial deformity; better prognosis than other forms
• Multicentric: Generalized lymphadenopathy; FeLV-associated

Cell size:

• Small cell (lymphocytic): Indolent; chronic signs; excellent response to chlorambucil + prednisolone
• Large cell (lymphoblastic): Aggressive; acute signs; requires CHOP; guarded prognosis

FeLV/FIV testing: All cats with suspected lymphoma. FeLV is strongly associated with mediastinal and multicentric forms.

Imaging:

• Chest radiographs (mediastinal mass, pleural effusion)
• Abdominal ultrasound (thickened bowel, mesenteric lymph nodes, renomegaly)

Cytology / Histopathology:

• FNA: Good for confirming lymphoma in masses, lymph nodes, effusions
• Biopsy: Required for GI lymphoma to differentiate small cell from large cell and from IBD

Immunohistochemistry / PARR:

• Clonality testing to confirm neoplasia vs reactive lymphoid hyperplasia
• Especially useful for small cell GI lymphoma vs IBD

Staging (WHO): I = single node; II = regional nodes; III = generalized nodes; IV = liver/spleen; V = blood/bone marrow/CNS.

Alimentary lymphoma:

• Small cell: Chlorambucil 2 mg PO q48-72h + prednisolone 1–2 mg/kg PO q24h → median survival 1.5–2.5 years
• Large cell: CHOP protocol (cyclophosphamide, doxorubicin, vincristine, prednisolone) → median survival 6–9 months

Mediastinal lymphoma:

• CHOP chemotherapy; thoracocentesis if effusion
• FeLV-negative cats have better prognosis than FeLV-positive

Renal lymphoma:

• CHOP; guarded prognosis (median 3–6 months); CNS prophylaxis recommended (CNS is common relapse site)

Nasal lymphoma:

• Radiation ± CHOP; best prognosis of all forms (median 1.5–3 years)

Prednisolone alone: 2–4 month survival; use only if owner declines chemotherapy or for palliation.