ADT Break May Benefit Responders in Metastatic Prostate Cancer

Metastatic prostate cancer, particularly in its hormone-sensitive stage, is primarily managed with androgen deprivation therapy (ADT). This treatment aims to reduce androgen levels, thereby inhibiting the growth of prostate cancer cells. While effective, continuous ADT is associated with a range of adverse effects, including fatigue, hot flashes, sexual dysfunction, bone mineral density loss, and metabolic changes, which can significantly impair a patient's quality of life. The clinical dilemma has long centered on balancing therapeutic efficacy with the burden of treatment-related toxicity. This has led to the exploration of intermittent ADT as a strategy to mitigate these adverse effects without compromising oncological outcomes.

The rationale for intermittent ADT

The concept of intermittent ADT involves cycles of ADT administration followed by treatment breaks, typically guided by prostate-specific antigen (PSA) levels. The hypothesis is that these breaks allow for recovery from ADT-induced side effects, potentially improving patient quality of life, while the reintroduction of ADT upon PSA rise maintains disease control. This approach also theoretically delays the development of castration-resistant prostate cancer by allowing androgen-sensitive cells to repopulate during the off-treatment period, thereby reducing selective pressure for resistant clones. However, the primary concern has always been whether such an approach could maintain the survival benefits seen with continuous ADT.

Clinical trials have investigated the non-inferiority of intermittent ADT compared to continuous ADT. These studies typically involve an initial induction phase of continuous ADT, usually for 6-9 months, to achieve a significant reduction in PSA. Patients who achieve a predefined PSA nadir (e.g., <4 ng/mL or <0.2 ng/mL) are then randomized to either continue ADT or enter an intermittent regimen. In the intermittent arm, ADT is discontinued until the PSA rises above a predetermined threshold (e.g., 10-20 ng/mL), at which point ADT is reinitiated. Treatment continues until the PSA again falls to the nadir, or for a fixed period, before another break is considered.

Key findings from these trials have generally demonstrated that intermittent ADT is non-inferior to continuous ADT for overall survival in carefully selected patients with metastatic hormone-sensitive prostate cancer. For instance, one large randomized controlled trial involving over 1,500 patients found no statistically significant difference in overall survival between intermittent and continuous ADT arms (hazard ratio for death 1.02, 95% confidence interval 0.91-1.14, p=0.74). This trial specifically included patients who achieved a PSA nadir of less than 4 ng/mL after 7 months of initial ADT. While overall survival was comparable, patients in the intermittent ADT arm reported improved quality of life metrics, particularly concerning sexual function, physical function, and fatigue, during the off-treatment periods. The median time off treatment in these studies has varied, but typically ranges from 6 to 12 months per cycle, offering substantial periods of relief from ADT side effects.

However, it is important to note that not all patients are suitable candidates for intermittent ADT. Patients with high-volume metastatic disease or those who do not achieve a significant PSA response during the induction phase may not derive the same benefits and could potentially experience worse outcomes with an intermittent approach. The decision to pursue intermittent ADT should be individualized, considering disease burden, PSA response, patient preference, and the potential impact on quality of life. Regular monitoring of PSA levels and clinical symptoms is essential to guide treatment decisions in the intermittent setting.