A Collision Tumor with Squamous Cell Carcinoma of Skin Overlying Breast and Invasive Breast Carcinoma

Invasive breast cancer is the most common carcinoma in women. Invasive ductal carcinoma, not otherwise specified (NOS), is the largest group of invasive breast cancers. The second most common cancer of skin is squamous cell carcinoma (SCC). Collision tumor is a very rare and unusual tumor. It is defined as the concrescence of two distinct primary neoplasms at one site. Herein, we report a 56-year-female patient who had a collision tumor in the right breast, composed of moderately differentiated squamous cell carcinoma (SCC) and invasive breast carcinoma NOS. In the literature, collision tumors in the breast are very rare and reported in various combinations, but there is only one reported case with SCC and invasive breast cancer, the same as in our case.