The landscape of metastatic castrate-resistant prostate cancer (mCRPC) treatment is evolving with the emergence of Bipolar Androgen Therapy (BAT), a novel approach that challenges traditional androgen deprivation strategies. BAT involves rapid cycling between supraphysiologic and near-castrate serum testosterone levels, targeting a unique vulnerability in prostate cancer cells that develop resistance to conventional treatments.
The therapy works by exploiting cancer cells' adaptation to low testosterone environments. When exposed to chronic low testosterone conditions, prostate cancer cells significantly upregulate their androgen receptor activity - increasing receptor levels by 30 to 90-fold compared to normal prostate cells. This adaptation, while enabling castration resistance, paradoxically creates a therapeutic vulnerability to supraphysiologic testosterone exposure.
Key Clinical Trial Results
The phase II TRANSFORMER trial, published in The Journal of Clinical Oncology, compared BAT to enzalutamide in 195 men with mCRPC who progressed after abiraterone treatment. The study demonstrated equivalent progression-free survival of 5.6 months for both treatments (HR: 1.13, p = 0.45) and comparable overall survival (BAT: 33 months vs. enzalutamide: 29 months; HR: 0.95, p = 0.80).
Notably, the trial revealed interesting crossover effects. Patients who switched to enzalutamide after BAT showed significantly better responses than those who switched to BAT after enzalutamide, with PSA50 responses of 77.8% versus 23.4%, respectively.
Novel Combination Approaches
Recent studies have explored BAT's potential in combination with other therapies. The COMBAT trial, investigating BAT with nivolumab in heavily pre-treated mCRPC patients, achieved its primary endpoint with a 40% PSA50 response rate (95% CI: 25.7-55.7%, p = 0.02). The combination demonstrated manageable toxicity with only 11% experiencing grade 3 adverse events.
Another promising direction emerged from a phase II trial combining BAT with olaparib, showing a 47% PSA50 response rate and median progression-free survival of 12.6 months. However, careful patient selection is crucial due to observed cardiovascular events in some participants.
Safety Profile and Implementation
BAT has demonstrated an acceptable safety profile, with most adverse events being manageable. The treatment can be administered using testosterone cypionate at 400 mg intramuscularly every 28 days, while maintaining continuous testosterone suppression through standard methods.
Common side effects include musculoskeletal pain, peripheral edema, and sexual side effects such as hot flashes and breast tenderness. Compared to enzalutamide, BAT showed fewer constitutional symptoms like fatigue, depression, and anxiety.
Future Directions
While BAT shows promise, its exact place in the mCRPC treatment paradigm remains under investigation. Several ongoing trials are exploring various combinations and sequences, including:
- STEP-UP: investigating BAT and enzalutamide sequencing
- APEX: examining BAT with Difluoromethylornithine
- BATRAD: studying BAT combined with Radium-223
- AcroBAT: evaluating oral testosterone administration
Biomarker analysis from the TRANSFORMER trial suggests that androgen receptor alterations in circulating tumor DNA might help identify patients most likely to benefit from BAT, potentially enabling more personalized treatment approaches.
The therapy represents an innovative approach to treating mCRPC, particularly for patients who have exhausted standard treatment options. While current NCCN guidelines don't yet include BAT as a standard treatment option, ongoing research into combination strategies may eventually establish its role in the therapeutic arsenal against advanced prostate cancer.
