Metastatic CD138+ Lobular Breast Carcinoma Mimicking a Plasma Cell Neoplasm

Abstract

Abstract We present a case of an 85-year-old female who received a bone marrow biopsy for concern over myelodysplastic symptoms and was subsequently diagnosed with a CD138-positive metastatic lobular breast carcinoma that mimicked a plasma cell neoplasm. Her medical history included endometrial serous adenocarcinoma (pT1a N0), severe mitral regurgitation, and atrial fibrillation. She presented with a 3-month history of thrombocytopenia (60,000/mcL) and a down-trending macrocytic anemia (nidus hemoglobin: 6-7 g/dL) that prompted a bone marrow biopsy. The aspirate smears were aparticulate and hemodiluted, while the touch preparations revealed a homogeneous population of large, plasmacytoid cells. These were again seen filling the medullary cavity on the bone marrow biopsy with eccentrically placed nuclei containing nucleoli and abundant eosinophilic cytoplasm. The cells were CD138, cytokeratin 7 and 8/18, mammoglobulin, and GATA-3 positive. They were cytokeratin 20, TTF-1/Napsin, PAX-8, and uroplakin negative. Further testing revealed the cells to be estrogen receptor positive (strong, 90%+), progesterone negative, HER2 negative, p120 positive (strong cytoplasmic), and E-cadherin negative. The patient’s prior serous adenocarcinoma histomorphology was not consistent with the plasmacytoid cells. Prior literature revealed a case report on a metastatic lobular carcinoma to bone marrow and discussion on the morphologic similarities, but the case was CD138 negative. This case highlights that CD138 can be positive in certain carcinomas, some of which can have a plasmacytoid morphology. Suspicion should be raised in an elderly female population.