Coincidental or causal? Concurrence of colorectal carcinoma with primary breast cancer

Multiple primary malignant neoplasms (MPMN) represent the occurrence of a second malignancy in the same patient within 6 months after the detection of first primary (synchronous) tumor, or > 6 months after primary detection (metachronous). We present a case of a patient treated for carcinoma of the breast who developed a metachronous primary malignancy in the colorectal tract. These tumors were histologically different with distinct immune-histochemical parameters. The association between breast and colon cancer is well documented in the literature with several studies reporting the coexistence of common extrinsic and genetic predisposing factors. Although rare, MPMN are becoming more common due to the increased number of elderly cancer survivors, improved diagnosis and enhanced awareness. The association between colorectal and breast cancer should not be dismissed merely as metastasis since there is good precedent for the co-occurrence of these primary tumors.