Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

Background Radium‐233 dichloride is an alpha emitter that specifically targets bone metastases in prostate cancer. Results of a previously reported phase III randomized trial showed survival benefit for radium‐223 compared to best supportive care in castration‐resistant prostate cancer (CRPC) with bone metastases. However, real‐world data are also needed with wider inclusion criteria. Methods We report results of a retrospective multicenter study including all patients with metastatic CRPC treated with radium‐223 in all five university hospitals in Finland since the introduction of the treatment. We identified 160 patients who had received radium‐223 in Finland in 2014–2019. Results The median overall survival (OS) was 13.8 months (range 0.5–57 months), and the median real‐world progression‐free survival (rwPFS) was 4.9 months (range 0.5–29.8 months). Alkaline phosphatase (ALP) values within the normal range before and during the radium‐223 treatment or the reduction of elevated ALP to normal range during treatment were associated with better OS when compared to elevated ALP values before and during treatment (p < 0.0001). High prostate‐specific antigen (PSA) level (≥100 μg/L) before radium‐223 treatment was associated with poor OS compared to low PSA level (<20 μg/L) (p = 0.0001). Most patients (57%) experienced pain relief. Pain relief indicated better OS (p = 0.002). Radium‐223 treatment was well tolerated. Toxicity was mostly low grade. Only 12.5% of the patients had grade III–IV adverse events, most commonly anemia, neutropenia, leucopenia, and thrombocytopenia. Conclusion Radium‐223 was well tolerated in routine clinical practice, and most patients achieved pain relief. Pain relief, ALP normalization, lower baseline PSA, and PSA decrease during radium‐223 treatment were prognostic for better survival. The efficacy of radium‐223 in mCRPC as estimated using OS was comparable to earlier randomized trial in this retrospective real‐world study. Our results support using radium‐223 for mCRPC patients with symptomatic bone metastases even in the era of new‐generation androgen receptor‐targeted agents.