Metastatic "Ductal Carcinoma In Situ-Like" Lobular Carcinoma in a Lymph Node: A Case Report and Review of the Literature.

Metastatic breast cancer resembling ductal carcinoma in situ (DCIS) is a rare phenomenon. In this article, we present a unique case of metastatic lobular carcinoma with DCIS-like morphology in the left axillary lymph nodes of a 52-year-old female. She presented with 2 lesions in the left breast on mammography, and a mastectomy with axillary lymph node dissection was performed. Gross examination showed a 3.5 × 2.5 × 1.0 cm indistinct tumor in the lower outer quadrant and a 2.5 × 2.5 × 1.8 cm tumor in the upper outer quadrant. Microscopic assessment revealed a pleomorphic lobular carcinoma in the lower outer quadrant and a grade 2 invasive ductal carcinoma in the upper outer quadrant. Sixteen of the 17 axillary lymph nodes showed metastatic lobular carcinoma with foci of solid and comedo-type DCIS-like features. Immunohistochemical analysis of the primary and metastatic lobular carcinoma showed no expression of E-cadherin and p63 antibodies. To our knowledge, metastatic lobular carcinoma exhibiting this pattern has not been reported. The case suggests that lobular carcinoma can morphologically recreate a primary microenvironment at a distant site and simulate in situ growth. Recognition of this pattern is important to avoid misdiagnosis.