Purpose: To investigate whether prostate-specific antigen PSA doubling time (PSADT) is constant in men with biochemical prostate cancer relapse after external beam radiotherapy (EBRT).
Methods and materials: A total of 513 men treated radically with EBRT, with or without androgen ablation (AA), between 1993 and 2000, developed biochemical relapse. The slope of the ln (PSA) vs. time graph is calculated for the first two values after PSA nadir (first slope), the last two recorded PSAs (last slope), and all values excluding the first and final PSA (mid slope). Differences in these slopes were compared statistically with subgroup analysis for AA and secondary intervention.
Results: For men treated with EBRT and AA first slope was faster than either mid slope (p = 0.031) or last slope (p < 0.001). Men treated with EBRT alone had no change in PSADT over time unless they subsequently received secondary intervention. This group had a more rapid last slope compared with mid slope (p < 0.001).
Conclusions: PSA initially rises more rapidly after AA cessation, probably because of testosterone recovery. A subgroup of patients, who received secondary intervention after treatment with radiotherapy alone, showed a change in PSADT, to a faster velocity. This greater than constant exponential PSA growth is presumably the catalyst for secondary intervention. Otherwise, PSADT did not change during prostate cancer biochemical relapse.