In contrast to marrow micrometastasis, development of symptomatic bone marrow involvement (bone marrow carcinomatosis, BMC) is a rare event in the course of metastatic breast cancer; published evidence on the outcome with systemic treatment is even more scarce. The objective of this study was to provide our institution's experience with the clinical presentation, prognosis, treatment, and associated complications of marrow involvement in breast cancer.

Twenty-two breast cancer patients with BMC diagnosed between 1995 and 2009 were analyzed.

All patients presented with osseous metastases at the time of diagnosis of BMC. Anemia was the most prominent hematologic sign present in 17/22, followed by thrombocytopenia. Cytotoxic treatment was offered to 21/22 of patients. The majority showed an improvement of cytopenia following treatment (10 out of 14 anemic patients, 6 out of 9 thrombocytopenic patients, all 4 leukopenic patients). The complication rate was acceptable, with only 5 grade 3 or 4 events related to cytopenia (febrile neutropenia, bleeding). The estimated median overall survival from the date of BMC diagnosis was 19 months. After 4 years, 4 of the patients were still alive. Interestingly, prognosis from the time of first diagnosis of BMC was independent of the duration of metastatic disease before BMC had been diagnosed.

Bone marrow involvement has to be considered in breast cancer patients, in particular in those with bone metastases and otherwise unexplained cytopenia. The peripheral blood smear can serve as a simple diagnostic tool, but the extent of erythroblastosis is not correlated with survival. Even with severe BMC-associated cytopenia, aggressive combination treatment regimens are indicated, since most patients show improved marrow function after chemotherapy and long-lasting survival is possible.