Adenoid cystic carcinoma of the prostate: an unusual subtype of prostate cancer

Adenoid cystic carcinoma (ACC) of the prostate is an extremely rare disease that arises from the basal cells of prostate acini and presents a poor prognosis for metastatic cases. Multiple treatment options exist for different stages of prostate cancer that include prostatectomy, radiation therapy, chemotherapy, and hormone therapy with gonadrotropin-releasing hormone (GnRH) agonists and antagonists for androgen receptor (AR)-positive cases. Although ACC has a biological potential that allows metastasis in a few cases; the current treatment option consists primarily of surgical resection along with close, long-term follow-up. Herein, we report this rare entity in a 79-year-old man who presented with liver metastasis. The tumor expressed GnRH receptor (GnRHR) and a very low level of Programmed death-ligand 1 (PD-L1). Immunohistochemical analysis revealed that the primary tumor was highly proliferative and AR-negative. We employed a clinically validated technology that utilizes patient's tumor and blood to recreate the tumor microenvironment ex vivo . After the diagnosis, we used the platform to test the efficacy of degarelix (a GnRHR antagonist), atezolizumab (a PD-L1 antagonist) and paclitaxel + carboplatin chemotherapeutic regimen. The assay output predicted response with chemotherapeutics and degarelix, without any sign of efficacy for PD-L1 antagonist. On the basis of these data, the patient was treated with paclitaxel + carboplatin combination chemotherapy first and showed clinical and radiological response as predicted by the ex vivo platform. After 4 cycles of chemotherapy, the patient received maintenance therapy with degarelix and demonstrated a favorable clinical response. Taken together, our results not only showed the accurate prediction Page 456 Julka et al. J Transl Genet Genom 2020;4:455-63 I http://dx.doi.org/10.20517/jtgg.2020.46 of clinical outcome but also demonstrate the rational selection of a regimen as a viable option for such a clinically challenging disease.