[Migration of nevus cells into the lymph nodes]

We report on an extremely rare case in which clusters of nevus cells have been found not only in the capsule but also in the central sinus of the lymph nodes. In a 52-year-old female who underwent a left radical mastectomy because of breast cancer, some resected lymph nodes were found to contain clusters of nevus cells. The following mechanisms to explain this phenomenon are possible. The first possibility may be a remnant that persisted during the course of embryogenesis. The another possible mechanism may be the migration of nevus cells into the lymph nodes. In other words the nevus cells might have been transported through the lymphatic essels as a "benign metastasis".