Lymphoma represents a malignant disorder resulting from abnormal multiplication of lymphoid tumor cells. A 4-year-old female mixed-breed dog was brought in due to a single swollen lymph node. On physical examination, there was a marked enlargement of the right prescapular node together with visible abdominal distention. The complete blood profile indicated pronounced lymphocytosis, and the peripheral smear revealed numerous lymphoblasts as well as Mott cells. Fine-needle aspiration of the affected node demonstrated that the cell population consisted mainly of lymphoblasts and Mott cells. These cytologic and hematologic results supported the diagnosis of a leukemic-phase, multicentric B-cell lymphoma showing Mott cell differentiation. PCR for antigen receptor rearrangement and flow cytometric analyses confirmed the occurrence of cross-lineage rearrangement (CLRA) and lineage infidelity (LI), respectively. The animal was treated with a CHOP-based chemotherapy protocol; however, the neoplastic process advanced rapidly, and death occurred three months after initial presentation. B-cell lymphoma with Mott cell features (MCL) is scarcely mentioned in veterinary case reports and tends to follow an atypical course. To date, there are no previous descriptions of canine MCL presenting with both CLRA and LI. This paper outlines the clinical observations, diagnostic procedures, and therapeutic management of a case of MCL showing CLRA and LI.
