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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.

Background Deregulation of CDK4/6, cyclin D/P16 and retinoblastoma (Rb) are known aberrations in certain malignancies. There has been a recent interest in exploring the combination of letrozole and CDK4/6 inhibitors in recurrent ER+ ovarian cancers. Methods This study aimed to determine the frequency of expression of Rb1, P16 and ER in ovarian epithelial tumors by immunohistochemistry. Results Co-expression of all 3 markers studied was seen in 10 % of high grade serous carcinoma (HGSC) and low grade serous carcinoma (LGSC). Coordinate expression of Rb1+ and ER+ in HGSC and LGSC was seen in 67 % of grade 1/2 vs. 44 % of grade three tumors (p < 0.05). The reverse was true with positive P16 staining in 73 % of grade three vs. 32 % of grade 1/2 tumors (p < 0.001). Conclusions Coordinate pattern of Rb1+ and ER+ in HGSC and LGSC is 19 and 50 %, respectively. Rb1 and P16 show inverse expression pattern according to tumor grade with more frequent Rb1 in low grade vs. more frequent P16 in grade 3 tumors. These data provide a rational basis for clinical trials that aim to target these proteins.