Case Presentation: A 71 year-old female presented to the emergency department with six weeks of worsening nausea and emesis. Her symptoms were associated with anorexia, 10-pound unintentional weight loss, and urinary incontinence. Past medical history was significant for right-sided breast cancer, status post partial mastectomy and radiation, 25 years prior to presentation. Physical examination showed abdominal distention with a positive fluid wave. Laboratory studies revealed acute kidney injury, leukocytosis, and anemia. Computed tomography demonstrated diffuse metastatic disease, omental carcinomatosis, metastatic deposits on the pericardium, pleura, and serosa, and moderate ascites. Differential diagnosis included endometrial carcinoma and lymphoma. Omental biopsy was obtained and pathologic examination reported a poorly differentiated malignant neoplasm. On further investigation, the patient reported that she had a history of monoclonal gammopathy of undetermined significance (MGUS), diagnosed 5 years prior to presentation. Further stains and studies were performed on the omental biopsy and were consistent with plasma cell neoplasm. Bone marrow biopsy confirmed multiple myeloma.

Discussion: Multiple myeloma (MM) is a plasma cell neoplasm that accounts for 1% of all cancers and approximately 10% of all hematologic malignancies. Patients often present with anemia, bone pain, elevated creatinine, fatigue, hypercalcemia, and weight loss. Extramedullary plasmacytomas (EP) are seen in approximately 7% of patient with MM at the time of diagnosis and correlate with poor survival. High dose radiation in atomic bomb survivors and radiologists has been shown to be a risk factor for MM. However, the correlation between breast cancer irradiation and MM is unclear. On the other hand, therapeutic radiation has been associated with a high risk of secondary acute leukemia or lymphoma, but not usually MM. The most common causes of malignancy-related ascites are malignancies of the ovary, breast, colon, lung, pancreas, and liver. Hence, the clinical suspicion for MM in our patient was low, and a gynecologic malignancy was favored. The initial work up was negative and the omental biopsy was unequivocal due to contradictory morphology and immunohistochemical stain results. The additional history of MGUS highly increased the suspicion for MM and subsequent non-routine pathologic testing led to the final diagnosis of MM and EP.

Conclusions: Patients with malignancy-related ascites often present to the hospital with acute findings after chronic progression of their constitutional symptoms. We describe a rare case of malignancy-related ascites due to multiple myeloma with extramedullary plasmacytoma in a patient with a remote history of breast cancer. Our case highlights the important role of thorough history taking in patients who have unusual disease presentations of malignancy.