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

Abstract

Introduction: The 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.

Conclusion: Early 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.

Keywords: NKX3.1; androgen receptor; cancer of unknown primary.

Fig. 1

(a) Axial unenhanced CT demonstrates a well‐defined, 25‐mm soft tissue mass in the left para‐aortic region (arrowheads). (b) Arterial and (c) venous phase IV contrast‐enhanced CT images show avid, heterogeneous enhancement in the arterial phase followed by mild washout in the venous phase. The mass exhibited iso‐signal intensity on (d) T1‐weighted images, (e) moderate‐to‐high signal intensity on T2‐weighted images, and (f) high signal intensity on diffusion‐weighted images on MRI.

Fig. 2

HE and immunohistochemical staining of the retroperitoneal tumor. (a,b) An adenocarcinoma consisting of the tubular proliferation of columnar‐shaped tumor cells. The tumor cells were positive for (c) NKX3.1, (d) PSA, and (e) AR and (f) negative for PSMA. (g) The MIB‐1 index calculated by Ki67‐positive cancer cells was 28.5%.

Fig. 3

¹⁸F‐Fluorodeoxyglucose positron emission tomography/CT did not show abnormal uptake in (a) other organs and (b) the prostate on a whole‐body scan. (c) Prostate MRI did not show a significant abnormality. CT images showed recurrences in (d) the supraclavicular and (e) para‐aortic nodes 3 months after the resection of the primary lesion. (g) A follow‐up CT showed a significant reduction of the lesions after an 18‐month CAB therapy.