Incidentally Diagnosed Breast Cancer in a Patient with Rectal Cancer: A Case Report

The development of screening and therapeutic approaches has improved the prognosis of colorectal cancer(CRC) patients, leading to an expected increase in the incidence of second primary cancers (SPCs). CRC hasbeen correlated with several extracolonic SPCs, including malignancies of the small intestine, stomach, breast,and ovary. We report a case of a 50-year-old woman with a history of rectal bleeding who was diagnosed withrectal adenocarcinoma. She underwent total neoadjuvant therapy followed by abdominoperineal resection inthe colorectal surgery ward at Ghaem Hospital, Mashhad, Iran, in December 2023. Five months after surgery,a soft tissue mass (10*13 mm) in her left breast was incidentally detected on a chest computed tomographyscan. Suspecting breast cancer, she underwent mammography and a core needle biopsy, which confirmed thediagnosis. She subsequently underwent a left partial mastectomy, and pathological evaluation revealed invasiveductal carcinoma. This case highlights the importance of considering SPCs in CRC survivors. Regular followupis recommended for these patients to detect early signs of recurrence, progression, or the presence of SPCs,enabling prompt and appropriate treatment.