Objective: We present histopathologic and immunohistochemical characteristics and differential diagnosis as well as possible pathogenetic mechanisms of benign nevus cell aggregates in five cases detected in axillary lymph nodes in patients operated for breast carcinoma.

Material and Method: We examined axillary lymph nodes from 5 patients operated for breast carcinoma. Between August 1999 and January 2008. These lymph nodes were examined in detail with Hematoxylin and Eosin, anti-pancytokeratin, anti-S-100, and anti- Ki-67.

Results: Of the lymph nodes with nevus cell aggregates, two were sentinel and three were non-sentinel lymph nodes of standard axillary dissection. All the lesions were small-sized and located in the lymph node capsule. Of these, two displayed nevus cells with cytoplasmic melanin pigment. Benign morphologic features of the lesions and immunohistochemical findings aided in differentiation from metastasis from either a breast carcinoma or a malignant melanoma.

Conclusion: In spite of their rarity, keeping the existence of nevus cell aggregates in lymph nodes in mind, that nowadays we examine in an extreme detail, would help us avoid a misdiagnosis of metastasis.