Keratin 19 mRNA measurement to detect micrometastases in lymph nodes in breast cancer patients.

We have used polymerase chain reaction (PCR) to measure keratin 19 mRNA in order to detect breast cancer cells invading axillary lymph nodes. In a consecutive series of 125 patients with primary breast cancer, 75 patients had no evidence of lymph node involvement by conventional histology. A total of 530 lymph nodes from these patients were examined and 106 (20%) gave a keratin 19 product detectable by Southern hybridisation. This correlated with primary tumour size (P<0.001). These 106 nodes came from 23 patients. Thus, using this technique, 23/75 (30.6%) patients were found to have evidence of lymph node involvement who would otherwise have been designated lymph node negative.