Pancytopenia And Limbic Encephalopathy Complicating Immunotherapy For Clear Cell Endometrial Cancer With Microsatellite Instability-High (MSI-H)

BACKGROUND: Clear cell carcinoma of the endometrium (CCE) has a tendency to occur in a mismatch repair protein deficient molecular background. Treatment with immunotherapy can predict a favorable response. CASE PRESENTATION: We are presenting a 53-year-old female, diagnosed with CCE 17 years ago, who was treated initially with hysterectomy and left salpingo-oophorectomy, who relapsed a few months later, and was then treated with left pelvic mass excision and sigmoidectomy. Recently, the disease recurred as a retroperitoneal lymphadenopathy, which was resected but then relapsed locally, spread to the lungs, and progressed further after three lines of chemotherapy. On pathological review of the tumor, it was found to harbor loss of nuclear expression of MLH-1 and PMS-2. Based on a strong predictor of response to immunotherapy, pembrolizumab was tried. However, within a few days of the single dose of pembrolizumab, immune thrombocytopenia followed by pancytopenia, recurrent seizures, visual hallucination, and cerebellar signs consistent with limbic encephalitis developed, which were not responding to steroid and intravenous immunoglobulin. CONCLUSION: We are presenting a case of a CCE with deficient mismatch repair that developed two autoimmune side effects, pancytopenia and limbic encephalitis, within a few days of a single injection of pembrolizumab.