Immunotherapy in the treatment of rectal invasion by prostate cancer with focal neuroendocrine differentiation: a case report and literature review

Background: Incidences of rectal infiltration by prostate cancer (PCa) are reported to affect up to 12% of patients studied. PCa invading the rectum is prone to cause difficulty in defecation, bloody stool and pain, leading to a decline in patients' quality of life. Unfortunately, the prognosis for these patients is poor and the survival period is short. Total pelvic exenteration (TPE) has been demonstrated to mitigate pain and improve symptoms such as defecation difficulty, dysuria, and hematuria. However, most patients still harbor residual tumor and fail to exhibit any improvement in long-term survival.

Case description: Here, we present a case of PCa invading the rectum with focal neuroendocrine differentiation, characterized by clinical presentations of defecation difficulties and rectal bleeding. A TPE procedure was performed, with a whole exome sequencing (WES) assay indicating that the patient exhibited a high tumor mutation burden (TMB) and high microsatellite instability (MSI-H). Subsequently, the patient received androgen deprivation therapy (ADT) combined with adjuvant immunotherapy following the procedure. At the subsequent six-year follow-up, no local or systemic recurrence was observed, and the prostate-specific antigen (PSA) level remained undetectable.

Conclusions: This disease entity remains relatively rare in the literature. Accurate differential diagnosis is important. TPE combined with immunotherapy may improve the prognosis. It is of utmost importance to achieve an accurate differential diagnosis, which necessitates the collaboration of multiple disciplines and the performance of requisite tests, including immunohistochemistry and genetic testing.