Cytologically Suggested Vulvar Involvement in a Dog with Multicentric Lymphoma After a Nodal Response to CHOP-Based Chemotherapy, with Discordant Clonality Results: A Case Report

Involvement of the female reproductive tract is rare in canine lymphoma. A 9-year-old spayed female Maltese dog was presented with generalized lymphadenopathy. Cytology of a mandibular lymph node aspirate indicated large cell lymphoma, whereas PCR for antigen receptor rearrangement (PARR) of the same sample was polyclonal. Splenectomy confirmed splenic large cell lymphoma, classified as World Health Organization clinical stage IVa. After 12 cycles of a CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisolone)-based protocol, restaging computed tomography showed a marked reduction in all measurable lymph nodes, whereas gastric and subcutaneous nodules persisted. On Day 181 (168 days after the start of chemotherapy), vulvar swelling was noticed and progressed despite antimicrobial and anti-inflammatory treatment, together with inguinal lymphadenopathy. Disease progression was diagnosed by inguinal lymph node cytology, and rescue chemotherapy was started; however, the dog developed acute dyspnea and died two days later. Results reported after death showed a mixed monoclonal and polyclonal immunoglobulin heavy chain (IgH) pattern in the inguinal lymph node and a clonal IgH rearrangement in the vulvar aspirate, which was cytologically consistent with lymphoma. In dogs treated for lymphoma, vulvar swelling may reflect neoplastic infiltration, and PARR results may differ between samples obtained at different sites and time points.