Here, we report a case in which a 36-year-old patient suffering from infertility was diagnosed with Lynch syndrome-associated synchronous endometrial cancer and colon cancer, and persistently enlarged left iliac paravascular lymph nodes were detected after receiving sintilimab treatment, a programmed cell death 1 (PD-1) receptor inhibitor. The gene discussed is PDCD1; the disease is malignant colon neoplasm.