Benign lymph node inclusions mimicking metastatic carcinoma.

AIMS To draw attention to non-neoplastic inclusions in axillary lymph nodes removed from women with primary breast cancer which may be mistaken for metastases. METHODS Five examples of non-malignant inclusions were detected in axillary lymph nodes removed from women with mammary carcinoma. Immunohistochemical staining for CAM 5.2 and S100 markers, as well as morphological assessment were performed. RESULTS Three of the five cases comprised naevus cells and two heterotopic epithelial elements. One of each was initially mistaken for metastatic carcinoma. Naevus cells in the capsule of axillary nodes are often arranged as lines of small, round cells and may readily be misinterpreted as metastatic lobular carcinoma. Heterotopic epithelial elements, in the form of tubules, can easily be mistaken for metastasis from an infiltrating ductal carcinoma. CONCLUSIONS Awareness of the occasional occurrence of non-neoplastic nodal inclusions will help avoid misdiagnosis. If immunohistochemical markers for epithelial cells are used to screen lymph nodes for metastasis, such lesions could be detected more frequently. It is important to combine immunohistochemistry with morphological assessment and the use of a panel of antibodies in histological diagnosis.