An increasing number of patients with multiple primary cancers are encountered due to improved cancer detection, widespread cancer screening, and better cancer treatment. Here, we report such a patient without a family history of malignancies or a known genetic predisposition developing three primary malignancies of the rectum, breast, and kidney. A 63-year-old female who underwent an anterior resection for rectal cancer was detected to have an elevated carcinoembryonic antigen (CEA) level during a routine follow-up, 8 years after the initial surgery. Clinical examination revealed a left breast lump which was confirmed as invasive ductal carcinoma (pT3 pN0 cM0). Imaging and colonoscopy excluded a local recurrence. However, a right renal lesion suggestive of a renal cell carcinoma was detected (pT1a). She underwent left mastectomy with a sentinel lymph node biopsy and a right partial nephrectomy with a curative intent. Postoperatively, CEA levels declined to normal limits. Management of multiple primary malignancies poses a major challenge. A multidisciplinary approach and tailored decision-making for the individual patient help with the optimum outcome.