Novel case of androgen receptor-positive cancer of unknown primary without serum prostate-specific antigen elevation that became progression free in the long term after primary combined androgen blockade.

introductionThe prognosis of cancer of unknown primary is very poor. Such a prognosis can be improved by characterizing primary characteristics and developing tailored site-specific therapy, especially for androgen receptor-positive adenocarcinoma. However, in such cases without elevated prostate-specific antigen, the efficacy of androgen deprivation therapy is unclear. CASE PRESENTATION: Herein, we report a case that presented with a retroperitoneal cancer of unknown primary that was confirmed as an androgen receptor-positive adenocarcinoma without prostate-specific antigen elevation. Pelvic magnetic resonance imaging did not reveal any suspicious cancer lesions in the prostate. Furthermore, malignant cells were not present in a prostate biopsy specimen. In spite of the prostate-specific antigen level, on the basis of immunohistochemical analyses, including NKX3.1, the patient was first treated with androgen deprivation therapy, leading to long-term progression-free survival.

conclusionEarly androgen deprivation therapy based on immunohistochemical analyses might lead to a good outcome in androgen receptor-positive adenocarcinoma cancer of unknown primary patients regardless of prostate-specific antigen level.