Successful rescue treatment using chlorambucil for presumed recurrence of sinonasal lymphoma in a cat

CASE SUMMARY: A 12-year-old male neutered domestic shorthair cat presented with a 2-week history of serous unilateral nasal discharge, swelling of the nasal bridge and sneezing. Whole-body CT revealed a mass filling the entire right nasal cavity with lysis of the cribriform plate. The cat was diagnosed with sinonasal large-cell lymphoma based on cytopathological analysis, with PCR-based lymphocyte clonality testing showing a monoclonal population with rearrangement of the immunoglobulin heavy chain gene. The cat received radiotherapy with a dose of 30 Gy in seven fractions given three times weekly, and then cyclophosphamide, doxorubicin, vincristine and prednisolone (CHOP)-based chemotherapy was initiated soon after completion of the radiotherapy schedule. Despite this treatment, CT performed 4 months after radiotherapy revealed enlargement of the lesion in the right nasal cavity consistent with presumed progression of the cat’s lymphoma. The cat then received rescue chemotherapy with chlorambucil, which markedly reduced the size of the disease burden in the nasal and frontal sinus without severe adverse effects. At the time of writing, the cat was receiving chlorambucil for 7 months without any clinical signs suggestive of tumour relapse. RELEVANCE AND NOVEL INFORMATION: To our knowledge, this is the first case of feline sinonasal lymphoma with chlorambucil used as rescue chemotherapy. This case indicates that chemotherapy with chlorambucil may be a useful treatment option for cats with relapsing sinonasal lymphoma following radiotherapy and/or CHOP-based chemotherapy.