A 65-year-old woman was referred for further examination following positive results on a fecal occult blood test. Colonoscopy revealed type 0-Ⅱa cancer, with a lesion measuring 2 cm in diameter in the rectosigmoid colon, and type 5 cancer, with a lesion measuring 6 cm in diameter in the upper rectum. Computed tomography(CT)and positron emission tomography (PET)-CT revealed mesorectal lymph node metastases. Therefore, she was diagnosed with rectosigmoid colon cancer(Stage Ⅰ)and upper rectal cancer(Stage Ⅲa). However, PET-CT also revealed slight fluorodeoxyglucose uptake in the paraaortic and lateral lymph node lesions; hence, the possibility ofmetastasis could not be ruled out. Given that chemotherapy was restricted due to renal dysfunction, low anterior resection was performed as the first choice. Analysis of intraoperative frozen sections showed paraaortic and lateral lymph node metastases; thus, we performed lymph node dissection of these lesions. Pathological examination ofthe resected lymph nodes revealed that 21 of 37 lesions were cancer metastases. S-1 was administered as adjuvant chemotherapy for 5 months. Mediastinal lymph node metastases was suspected on chest CT 5 months and 3 years post-surgery; thus, panitumumab was administrated. These lymph nodes decreased in size immediately. Six years after the first surgery, the patient was well without any signs of recurrence.