(109) CONTEMPORARY HIGH-LEVEL RADIATION THERAPY PROSTATE CANCER TRIALS MAY UNDERESTIMATE THE RISK OF BIOCHEMICAL RECURRENCE

Abstract Introduction Prostate specific antigen (PSA) is an important tool for the diagnosis of prostate cancer and detection of biochemical recurrence (BCR) after treatment. Secretion of PSA is a testosterone (T) dependent process. When T levels are below saturation point, PSA levels may be artificially low. T recovery rates after ADT cessation are variable and often fail to normalize. Recent data suggest that PSA levels should be indexed to T levels. The Radiation Therapy Oncology Group (RTOG, now NRG) has performed numerous clinical trials of radiotherapy (RT) with androgen deprivation therapy (ADT) in this population. Objective We explored whether the RTOG trials have indexed post-treatment PSA to T levels. Methods The clinicaltrials.gov (CTG) website was reviewed for RT/ADT clinical trials run by the RTOG/NRG over the past decade. For studies with results, manuscripts were reviewed; for the others the CTG protocol was reviewed. Demographic, oncologic, and treatment characteristics such as age, baseline PSA, Gleason grade, and length of treatment were collected if available. Data were reviewed assessing for mention of T measurement at time of post-treatment PSA checking, as well as assay suggested and time of day adherence for T measurement. Results 15 clinical trials that met the study criteria were identified (Table). 14 029 patients have been enrolled. Median age was 64 (IQR [interquartile range] 2.5) years, median PSA was 0.5 (IQR 3.8), median Gleason grade group was 2 (IQR 1). 6/15 (40%) made no mention of T measurement whatsoever. None of the manuscripts published to date reported any T levels. One study had T recovery after ADT in the CTG results. Only 4/10 (40%) protocols stipulated that T should be measured concurrently with PSA, for an overall 27% T measurement performance rate. Only 1 protocol stipulated the type of assay and time of day (morning) measurement. 9/15 (60%) did not require regular follow up testosterone measurements for patients on ADT, while only 2/15 (13%) studies required a baseline T level to be measured. Conclusions Routinely indexing testosterone to PSA levels after high level RT/ADT trials is uncommon. This renders the BCR data unreliable, potentially underestimating BCR rates in these trials. Disclosure No.