The detection of breast carcinoma micrometastases in axillary lymph nodes by means of reverse transcriptase-polymerase chain reaction.

Background: The development of a sensitive method for the detection of breast carcinoma micrometastases in axillary lymph nodes is reported.

Methods: The method was based on amplification of MUC1 mRNA, which encodes a core protein of polymorphic epithelial mucin, by a reverse transcriptase-polymerase chain reaction (RT-PCR). Total RNA, which was extracted from a breast carcinoma cell line (MCF-7), primary breast carcinomas, and axillary lymph nodes, was subjected to analysis of MUC1 mRNA expression by the RT-PCR method.

Results: MUC1 mRNA expression was detected by RT-PCR in MCF-7 cells and in all 15 primary breast carcinomas but not in control lymph nodes taken from patients with benign diseases. A serial dilution study revealed that MUC1 RT-PCR was a very sensitive method, detecting one MCF-7 cell per 1,000,000 lymph node cells. The detection sensitivity of MUC1 RT-PCR method was compared with that of immunohistochemical staining of an epithelial marker (polymorphic epithelial mucin). Fifty axillary lymph nodes were obtained from 15 patients with primary breast carcinomas, and metastasis in each lymph node was investigated by both methods. The immunohistochemical method demonstrated metastasis in nine lymph nodes, and MUC1 mRNA was detected in all of them. Of the 41 lymph nodes that were diagnosed to be devoid of metastasis by immunohistochemistry, MUC1 mRNA was expressed by 6 but not by the other 35, indicating the presence of micrometastases in these 6 lymph nodes that could be detected only by the MUC1 RT-PCR method.

Conclusions: The MUC1 RT-PCR method is more sensitive than immunohistochemistry for the detection of micrometastases in axillary lymph nodes. This new method would be of practical value in selecting the patients at high risk for relapse from those who are histologically lymph node negative.