Introduction Although once very uncommon, multiple primary malignant neoplasms (MPMN) are becoming an increasingly popular subject in medical literature. With 182,000 new diagnoses per annum, breast cancer is the most frequently diagnosed cancer amongst women in the United States. Colorectal cancer remains the second most commonly diagnosed cancer in females, and the third in males worldwide. Methods In order to gather literature on synchronous and metachronous occurring breast and colon cancer, we searched PubMed using keywords such as 'colorectal cancer', 'breast cancer', and 'MPMN'. We searched through case reports, case series, clinical trials, letters to the editor, and retrospective series. We included any manuscript in English published between January 1990 and January 2019. The articles featured patients who had primary colorectal cancer with primary breast cancer. Articles featuring patients with more than two malignancies or malignancies other than colorectal and breast cancer were excluded. Furthermore, any metastatic cancers were excluded as well. This narrowed our search down from over 100 manuscripts to just four. Results Fortunately, the prognosis was found to be no different for these patients with MPMN assuming diagnosis and treatment are performed in a timely fashion. Additionally, it appears that although a patient with one primary cancer is at a greater risk for the development of a second cancer, it is still an odd phenomenon and thus an unlikely occurrence. Conclusion Detection of one cancer increases the odds of detecting another cancer. Hence, it is important to consider the possibility of a synchronous tumor in a patient with a newly diagnosed colon tumor, as well as to not only consider disease recurrence when following up post-resection.
Keywords: breast cancer; colorectal carcinoma; multiple primary malignant neoplasms.