Treatment of patients with metastatic hormone-sensitive (mHSPC) depends on androgen deprivation therapy (ADT) to inhibit androgen receptor (AR) signaling. Although the majority of patients respond well to ADT, castration-resistant prostate cancer (CRPC) inevitably develops. Addition of docetaxel, abiraterone acetate, or enzalutamide, to ADT significantly increases cancer-specific survival (CSS) [1–3]. The drawback is that not all patients respond to the therapies equally well and biomarkers to enable personalized treatment are urgently needed. Prostate-specific antigen (PSA) is a powerful biomarker for diagnosis of PC, but there are no validated biomarkers to prognosticate prognosis, let alone prediction of therapy response, of metastatic disease prior to ADT. Mechanisms important for resistance to ADT and development of CRPC include increased AR levels, constitutively active AR variants such as AR-V7, and intratumoral steroid production to sustain AR signaling despite castrate levels of steroids [4–7]. Although these changes mainly have been reported in CRPC, inherent expression could indicate predisposition for CRPC and poor response to ADT and other therapies targeting AR signaling.
To identify patients with optimal therapeutic benefit from drugs with conceptually different targets, their metastatic disease needs to be characterized. Given the difficulty to access metastatic tissue for analysis, circulating tumor cells (CTCs) have a potential to provide phenotypic information of the tumor, in addition to the prognostic value associated with their abundance [8]. We have demonstrated that gene expression in circulating tumor cells (CTCs) reflects the phenotype of prostate cancer metastases [9]. It has also been suggested that detection of AR-V7 mRNA and AR-V7 localization to the nucleus in CTCs predict poor response to drugs targeting the androgen signaling axis, such as abiraterone acetate and enzalutamide, in patients with CRPC [10,11]. Although the biomarker potential of CTCs mostly has been evaluated in CRPC [10,12,13], two studies have described the presence of CTCs as a prognostic marker for overall survival, progression-free survival (PFS), and time to CRPC also in mHSPC [14,15]. In addition, we previously showed that detection of EGFR mRNA in CTCs is a negative prognostic biomarker for CSS in mHSPC [16].
The present study investigates expression of genes associated with development of CRPC [17] for their prognostic value in mHSPC response to ADT. We showed that mRNA for the steroidogenic enzymes AKR1C3 and CYP17A1 can be detected in CTCs in high volume mHSPC, and that the detection of mRNA for AR-V7 in CTCs before ADT has prognostic value.
Taylor & Francis Group, 2019. Vol. 58, no 11, p. 1660-1664