A 13-year-old spayed female Beagle presented to a medical oncologist for a lingual mass. On physical exam, there was a 1 cm, slightly lobular, slightly ulcerated mass found in the middle of the tongue surface. The mass bled upon fine needle aspirate. The patient also had a history of an adrenal mass, a retroperitoneal mass, unspecified liver changes on an abdominal ultrasound, and possible Cushing’s disease. No evidence of metastatic disease was found upon chest radiographs. A fine needle aspirate was obtained and submitted for cytologic evaluation.
Submitted slides were moderately to very highly cellular and consist of many red blood cells and a nucleated cell population predominated by individual round cells with very low numbers of neutrophils and small lymphocytes. These round cells have a moderate amount of basophilic cytoplasm that occasionally contains a perinuclear clear area/prominent Golgi. The nuclei are most commonly eccentric, round to oval to rarely indented, and have a densely clumped to finely stippled chromatin pattern and indistinct nucleoli. Anisokaryosis is moderate. Binucleation is commonly noted; the two nuclei are typically eccentrically located together in the cell. Multinucleation (3-5 nuclei) are also occasionally found. The cytologic diagnosis was plasma cell tumor. See photos below.
Contrary to common misconception, definitive diagnosis of round cell tumors is typically easier with cytology in comparison to histopathology. The morphologic detail that differentiates mast cell tumors, histiocytomas, plasma cell tumors, lymphoma, and transmissible venereal tumors, is more apparent in cytologic preparations. The same round cell tumors can be differentiated histologically, but this commonly requires immunohistochemical or special stains.
The diagnosis was plasma cell tumor. This patient likely had a solitary extramedullary plasmacytoma, which is largely considered a benign neoplasm that can be cured with complete excision or radiation therapy (these tumors are typically cutaneous, but can arise from mucous membranes and essentially anywhere in the body). However, a metastatic lesion that is part of a more systemic, malignant plasma cell tumor originating from the bone marrow (multiple myeloma), cannot be ruled out. Further, even though most extramedullary plasmacytomas are considered benign, the potential for disseminated disease does exist. Lastly, the malignant potential of these cells cannot be determined based on their cytomorphology. As in this case, many benign solitary plasmacytomas exhibit multiple criteria malignancy (anisokaryosis, multinucleation); and, many of the plasma cells found in the marrow of multiple myeloma cases are very uniform in appearance. Therefore, when a plasma cell tumor is diagnosed, it is always prudent to evaluate the patient for metastasis via imaging and evaluation of serum globulins. If a hyperglobulinemia is present, a serum protein electrophoresis should be performed to determine if a monoclonal gammopathy is present.
Submitted by Casey J. LeBlanc, DVM, PhD, DACVP of KDL VetPath