A case report of small-cell carcinoma of the prostate with ectopic adrenocorticotropic-hormone (ACTH) syndrome and hypokalemia.

[BACKGROUND] Small-cell prostate cancer is the most common type of treatment-related neuroendocrine prostate cancer. It typically originates from prostate adenocarcinoma following prolonged endocrine therapy, presenting as desmoplasia-resistant. At this stage, indicators such as prostate-specific antigen (PSA) and androgen receptor (AR) remain within normal ranges, conflicting with widespread metastatic lesions. Simultaneously, neuroendocrine indicators exhibit a significant elevation. Small-cell prostate cancer can secrete hormones, leading to ectopic endocrine syndrome.

[CASE DESCRIPTION] In this context, we present a case wherein prostate adenocarcinoma transformed into small cell prostate cancer, accompanied by a rare paraneoplastic syndrome involving ectopic adrenocorticotropic-hormone (ACTH) production. The patient primarily presented with hypokalemia, edema, and hypertension. Following multi-line anti-tumor therapy and adrenal steroidogenesis inhibitors therapy, the patient's symptoms, including hypokalemia and edema, markedly improved. However, the patient ultimately succumbed to tumor progression. We present this case based on the CARE reporting checklist.

[CONCLUSIONS] Our case referred to the treatment regimen for small-cell lung cancer, suggesting that the treatment regimen for small-cell lung cancer is effective for small-cell prostate cancer, but tumors can quickly become resistant. The efficacy of adrenal steroidogenesis inhibitors in treating ectopic ACTH syndrome (EAS) is demonstrated, underscoring that judicious treatment decisions can effectively prolong patient survival and enhance their quality of life. We present this case series based on a list of AME case series reports.