Pamela Cheung

Prostate cancer (PCa) is the most common cancer and the second leading cause of cancer death in American men. Most patients with metastatic disease respond initially to androgen deprivation therapy (ADT) but almost inevitably progress to castration-resistant prostate cancer (CRPC). Identification of markers and drivers of Metastatic CRPC (mCRPC) that (a) represent a progenitor-type cancer cell population, (b) persist in castration-resistant disease, (c) are actionable targets expressed on the cell surface, and (d) are induced by hypoxia is required to facilitate the development of novel targeted therapies. We identified prostatic acid phosphatase (PAP), particularly the transmembrane form (TMPAP), as one such potential target. PAP is both a phosphatase and a 5′ectonucleotidase that generates adenosine. PAP is a human tumor marker first described in 1936 and is still used as an important prognostic marker for advanced metastatic prostate cancer. Our group recently reported that the transmembrane form of the protein (TMPAP) is expressed in CRPC and can serve as a potential therapeutic target. We identified a lead human anti-TMPAP antibody clone 3D8 (3D8-Ab). 3D8-ADCs (Antibody Drug Conjugates) and 3D8-Ab were tested for their ability to reduce tumor size/volume in a xenograft model. The human PAP-expressing PCa cell line VCaP, originally derived from a vertebral metastasis from a patient with CRPC, was inoculated subcutaneously into SCID mice. Treatment with either 3D8-Ab or 3D8-ADC significantly reduced tumor size and increased animal survival. These data indicate that targeting PAP with monoclonal antibodies either alone or conjugated to toxins has the potential to treat CRPC.

Background/Objectives: Metastatic Prostate Cancer (mPCa) is generally treated with systemic therapy. Many of these treatments, particularly androgen ablation, are not curative and cause substantial morbidity. Oligometastasis is defined as a limited number of metastatic deposits, whose disease does not seem to progress to a widespread distribution of cancer. There have been some reports of trials of localized treatment of PCa oligometastatic disease with curative intent. We herein report a case of oligometastatic prostate cancer treated primarily with surgical removal of metastases, which has no evidence of active disease twenty years post-operatively. Methods: Extensive retrospective chart review, immunohistochemical staining, growth rate calculations, and imaging studies were performed to trace the progression of this patient’s disease course. Results: A detailed investigation of biochemical markers of recurrence revealed normal-low prostate specific antigen (PSA) despite advanced disease, early rather than metachronous dissemination of metastases to distant sites, and hypoxia-conditioned phenotypic plasticity and memory in disseminated tumor cells (DTCs). Conclusions: This rare outlier case of oligometastatic prostate adenocarcinoma challenges traditional linear models of metastatic progression and clinical reliance on PSA as a marker for PCa detection and treatment in advanced cases. By investigating key questions regarding the identity, timing, and trajectory of DTCs, we propose a biologically informed narrative of this patient’s disease progression and a reconsideration of metastases directed therapy (MDT) of oligometastases as primary therapy in select patients.