Pancytopenia due to massive bone marrow carcinomatosis after radiotherapy for locally advanced breast cancer.

Pancytopenia is a rare complication among patients with breast cancer. Here, we report a case of pancytopenia due to massive bone marrow carcinomatosis (BMC) developed after local radiotherapy following to mastectomy. A 48-year-old woman with locally advanced breast cancer underwent mastectomy and axillary lymph node dissection. During adjuvant chemotherapy, rapidly growing supraclavicular lymph node metastasis was noted, so chemotherapy was discontinued and local radiotherapy was performed. There was no myelosuppression or systemic metastases prior to radiotherapy, but 2 weeks after the completion of radiotherapy, complete blood counts showed pancytopenia, and chest CT scans revealed multiple bone metastasis. A bone marrow biopsy was performed and massive BMC was diagnosed. Despite the best supportive care, her disease progressed rapidly and she died 2 months after radiotherapy. Locally advanced breast cancer that is resistant to chemotherapy is at risk of early fatal BMC and should be carefully monitored.