Advanced tumors lacking in mismatch repair (MMR) were very responsive to pembrolizumab which is a programmed death 1 ligand (PD-1) checkpoint inhibitor. In 2017, the U.S Food and Drug Administration skeptically permitted its usage since it was the only therapeutic option choice available at that time. Nevertheless, information available regarding the response checkpoint inhibitors in advanced endometrial cancer associated with the Lynch syndrome (LS) is exiguous, especially in uterine serous carcinoma which happens to be rare in Lynch syndrome. The researchers give an account of a patient’s case where the deficiency of MMR in the tumor revealed that the patient was suffering from metastatic uterine serous carcinoma, which happened because of a germline MSH6 alteration (Lynch syndrome). An incomplete response was experienced in 2018 when the patient was treated with first-line pembrolizumab. For over 2 years, she has stayed free of advancement and asymptomatic. The gene, p.F1088fs, was found to have an upstream physical alteration and a high mutational burden through tumor sequencing. The PD-L1 expression had negative immunohistochemical staining. The clinical qualities of the patient, her tumor’s molecular characteristics as well as the mechanism of the reaction of her tumor are analyzed in this article. Another point discussed here is the length of time taken for her immunotherapy.

A woman diagnosed with metastatic uterine serous carcinoma and Lynch syndrome because of a germline MSH6 alteration was shown to have an extended respite from the frontline single-agent pembrolizumab in this case. The early treatment of high microsatellite instability/hypermutated uterine cancers/MMR-deficient cancers in women who are diagnosed with Lynch Syndrome is indicated to have a clinically fundamental advantage if checkpoint inhibitors are utilized as single agents in the treatment.