A Collision Tumor in the Breast Consisting of Invasive Ductal Carcinoma and Malignant Melanoma.

Collision tumors are rare neoplasms that consist of at least two different cell lineages at the same site. Given the many possible combinations that can occur, collision tumors, while rare, have been reported in multiple locations such as the stomach, bladder, and thyroid. Collision tumors are rarely found in breast tissue, with only a few cases reported in the literature. We herein report a unique case of a 79-year-old woman with a history of melanoma who presented with a left breast mass that was subsequently found to have invasive ductal carcinoma (IDC) and metastatic melanoma in the breast tissue. This is one of the first reported combinations of these two malignancies.