Benefits from standalone durvalumab treatment in an elderly patient with advanced prostatic sarcoma: a case report.

There is a lacking of effective therapeutic strategies in the treatment of advanced prostatic sarcoma with high-frequency microsatellite instability (MSI-H) or mismatch repair deficient (dMMR). In this study, we present the first described a case of advanced MSI-H and dMMR prostatic sarcoma in elderly patients with multiple comorbidities, who received an anti-PD-L1 monoclonal antibody (durvalumab) as the first-line treatment and achieved partial remission (PR) without visible adverse events. A 91-year-old male patient presented with frequent urination and defecation difficulty for over three months, aggravating for ten days. Digital rectal examination showed the prostate gland was III° enlargement and tough with a smooth surface. The MRI showed occupying lesions in the prostate without distant metastasis. Then, the prostate biopsy showed poorly differentiated small round cell malignant tumor and considered prostatic sarcoma. Immunohistochemistry showed MSI-H and dMMR prostatic sarcoma. Durvalumab alone was applied at a cycle of every 21 days (500 mg/day) for 18 months and achieved PR two months since the treatment. During the treatment, we didn't observe rash, immune-related pneumonia, hepatitis, and other adverse events. Also, no recurrence or metastasis was observed until now. Durvalumab is effective and safe in the treatment of advanced MSI-H or dMMR prostatic sarcoma in an elderly patient. It is promising to be an available choice for advanced prostate sarcoma, which is unsuitable for surgery, conventional chemotherapy, and radiotherapy.