Contralateral axillary lymph node metastasis and molecular changes in second primary breast cancer: a case report.

Contralateral axillary metastasis (CAM) is rather rare in primary breast cancer. In this case, we present a 46-year-old female patient who underwent left breast-conserving surgery (BCS) and left axillary lymph node dissection (ALND). Two years later, an enlarged lymph node was found in her right axilla. Magnetic resonance imaging (MRI) of the breast displayed a left breast mass with multiple internal mammary lymph nodes and abnormal lymph nodes in the right axillary region. However, no abnormalities were found in the right breast. The left breast mass was diagnosed as invasive carcinoma by core needle biopsy. During the operation, we suggested that the contralateral lymph nodes were metastatic from the second primary breast cancer by preoperative 99mTc injection around the left breast. The patient underwent left mastectomy and right axillary lymph node dissection. The postoperative pathology was diagnosed as metachronous secondary primary left breast cancer, in which the initial presentation was lymph node metastasis to the contralateral axilla of the left breast. Therefore, we propose that CAM may be more common in second primary or recurrent breast cancer. It should be treated as locoregional extension. Preoperative lymph node markers are important to identify whether contralateral axillary lymph node metastasis occurs from a second primary breast cancer.