Introduction/Background Lynch syndrome is a secondary cause for hereditary ovarian cancer after BRCA mutation. Germline mutations in the DNA-mismatch repair genes cause tumorigenesis and a high immunogenicity. Recent studies showed a promising use of immunotherapy in MMR deficient (MMRd) tumors. We present a case of a patient with LS associated OC and a complete response to pembrolizumab.

Methodology x

Results A 44-year old patient was admitted to the hospital with lower abdominal pain. The patient’s history showed LS with a germline mutation in the MSH2-gene. Initial diagnostics showed a pelvic tumor mass and a highly elevated cancer antigen 125. After debulking surgery, histopathological findings showed a high grade serous OC with a mutation in the MSH2 and MSH6-genes. Only 5 weeks after operation with no residual tumor mass a quick and significant intraabdominal progression of the disease was diagnosed. Adjuvant therapy with carboplatin and paclitaxel in a weekly course did not lead to sustainable response. An anti-PD-L1 antibody therapy with pembrolizumab was initiated. After only 2 courses of therapy the laboratory results and clinical status of the patient improved tremendously. Shortly after a complete response was detected and until today for 28 cycles immune checkpoint inhibition therapy is ongoing. The patient remains tumor free for 21 months now.

Conclusion Recent studies suggest a promising effect of checkpoint inhibition within MMRd tumors. OC on the other hand does not seem to show an overall good response to immunotherapy. The significance of germline compared to somatic mutations has not yet been investigated in prior studies suffiently. To our knowledge, this is the first case with complete response to checkpoint inhibition in OC associated with LS. Comprehensive testing for germline mutations should be established. Regarding Lynch syndrome associated ovarian cancer, immune checkpoint inhibition is an efficient therapy in tumors nonresponsive to standard therapy.