Low and slow.

Top Line: Understanding post-treatment PSA kinetics is key to deciphering when to pull the trigger on unpopular salvage therapies for prostate cancer.

The Study: When it comes to radiation, we’re learning our expectations may need to be redefined following brachytherapy and/or ultra-hypofractionated external beam techniques. Here’s another large multi-institutional retrospective review evaluating PSA kinetics after the above radiation modalities. Included are 3500 men, half with low and half with favorable or unfavorable intermediate risk prostate cancer, treated at 10 institutions since 1990 with definitive ultra-hypofractionation (49%) or low- (36%) or high- (15%) dose rate brachy. In line with previous reports, median PSA nadir across all three modalities was ≤0.2, and this was significantly impacted by risk category but not by treatment. Median time to nadir was also similar at around 3-4 years: 44 months after ultra-hypofractionation, 51 months after low-dose rate brachy (side note: nadirs thought to be lowest and slowest here due to continued radioisotope decay over several months), and 37 months after high-dose rate brachy. Rates of sustained (read: not bouncing) biochemical recurrences of ≥2.0 above nadir were similarly low across modality, but again the authors note a strong correlation between freedom from biochemical failure at 4 years (88% of entire population) and long-term freedom from the same. Finally, overall, only 4% proved to have sustained biochemical recurrences by 2 years so an initial early rise in PSA should be assumed a bounce until subsequently proven otherwise.

TBL: We have confirmatory evidence that ultra-hypofractionation and brachytherapy as definitive treatment for low/intermediate risk prostate cancer provide virtually equal rates of ablation-level PSA nadirs and of (excellent) long-term biochemical control. | Levin-Epstein, Radiother Oncol 2020