Contemporary prostate cancer radiation therapy trials may underestimate the risk of biochemical recurrence

Radiotherapy is often given with androgen deprivation therapy for prostate cancer which causes a reduction in testosterone levels, which when below castrate levels, can cause the prostate specific antigen (PSA) levels to be artificially low.

To determine if high-level radiotherapy clinical trials are underestimating biochemical recurrence (BCR) rates due to inadequate measurement of testosterone levels.

The study plans for clinical trials performed by the Radiation Therapy Oncology Group (RTOG [now NRG]) on clinicaltrials.gov were reviewed for details on testosterone measurement in trials from 1994 to 2023, namely if the testosterone levels were indexed to PSA levels.

PSA being indexed to testosterone levels and other metrics of testosterone measurement, including time of day of measurement, assay used, and mean testosterone measurement.

Five of 21 (24%) trials stipulated that testosterone levels should be indexed to PSA levels. Eleven of 21 (52%) trials made no mention of testosterone. No trial reported testosterone assay or time of day of measurement. Thirteen of 21 (62%) trials did not require regular follow-up testosterone measurements.

The number of clinical trials indexing or regularly measuring testosterone was surprisingly low, which could cause an underestimation of BCR rates.

Strengths include being the first study, to our knowledge, to analyze the details of testosterone measurement in high-level radiotherapy trials. Limitations include only analyzing RTOG/NRG trials, analyzing unpublished data, and using clinicaltrials.gov rather than official trial protocols to determine details of testosterone measurement.

Indexing of testosterone levels to PSA levels in high-level radiotherapy trials using androgen deprivation therapy was uncommon, possibly rendering data on BCR unreliable, potentially underestimating BCR rates.