Ileocecocolic B-Cell Lymphoma Mimicking an Intestinal Neuroendocrine Tumor in a Cat: A Diagnostic Pitfall.

An 8-year-old, 3.3 kg spayed female Korean Shorthair cat presented with chronic vomiting, waxing and waning hyporexia, and weight loss. Ultrasonography revealed a 1.5 × 1.6 cm ileocecocolic junction (ICCJ) mass and multiple colonic nodules. Fine-needle aspiration biopsy yielded predominantly oval cells with loosely cohesive clustering, and an intestinal neuroendocrine tumor (NET) was favored. Segmental resection of the distal ileum, ICCJ, and proximal colon with stapled side-to-side ileocolic anastomosis was performed. Histopathology also favored NET because the lesion consisted of relatively monomorphic round-to-polygonal cells with eosinophilic to chromophobic granular cytoplasm. Neoplastic cells showed strong CD20 immunoreactivity and nuclear PAX5 labeling but lacked CD3 immunoreactivity, with CD3-positive lymphocytes mainly peripheral to the neoplastic population. Labeling for chromogranin A, synaptophysin, and NSE was absent. These findings led to reclassification as B-cell lymphoma with NET-like morphology, most consistent with an intermediate-cell type. Postoperatively, vomiting improved and resolved after cyclophosphamide, doxorubicin, vincristine, and prednisolone-based chemotherapy was initiated. At approximately 6 months after surgery, body weight remained stable, no postoperative complications were identified, and no discrete recurrent mass was detected. This case demonstrates that feline enteric B-cell lymphoma may rarely exhibit NET-like morphology and be misclassified on cytology and routine histopathology without immunophenotypic confirmation.