Bone marrow micrometastases in primary breast cancer: prognostic significance after 6 years' follow-up.

Using an antiserum to epithelial membrane antigen we have screened multiple bone marrow aspirates from 350 patients with primary breast cancer taken at the time of initial surgery. 89 (25%) patients were found to have micrometastases and their presence was related to pathological size (P less than 0.01), the presence of peritumoral vascular invasion (P less than 0.001), and positive lymph nodes (P less than 0.005) but not menopausal status. At a median follow-up of 76 months (range 34-108) 107 patients had relapsed with distant metastases. 48% (43 of 89) of these patients had micrometastases initially compared with 25% (64 of 261) who did not (P less than 0.005). The test predicts for relapse in bone (P less than 0.01) and other distant sites excluding bone (P less than 0.001) and is associated with a shorter overall survival (P less than 0.005). We conclude that the detection of micrometastases signals a high likelihood of early relapse and decreased survival in breast cancer.