Prostate-specific antigen doubling times are similar in patients with recurrence after radical prostatectomy or radiotherapy: A novel analysis

Purpose: Some investigators have analyzed the rate of growth of prostate cancer that has recurred after definitive radiotherapy or radical prostatectomy using serum prostate-specific antigen (PSA) doubling times (DT). We examined all PSA values in recurrent patients to determine the pattern and rate of increase in PSA after radiation therapy and radical prostatectomy. Patients and Methods: Charts of 96 recurrent radical prostatectomy patients (mean age, 62.8 years; range, 47 to 76) and 42 recurrent radiation therapy patients (mean age, 67.2 years; range, 52 to 83) were reviewed. All available PSA values between the date of operation/radiation treatment and last follow-up evaluation or the initiation of second-line therapy are included. Rate of PSA DT was not assumed to be constant over time; it was instead allowed to vary. We use a piecewise linear random-coefficients model in time for log(PSA), which allowed different mean models for both treatments. Results: The PSA DT in the first year after radiation therapy was -1.17 years, which reflects the continuous decline in PSA in the average patient during the first year after radiotherapy despite eventual biochemical progression. In contrast, the PSA DT in the radical prostatectomy group was 0.66 in the first year. In year 2, after radiation therapy, the PSA DT was lengthy at 1.82 years, significantly longer (P = .0025) than in the radical prostatectomy group (0.76 years). After year 2, there were no significant differences between the two groups (P > .05). Conclusion: A piecewise linear random-coefficients model enables interval analysis of PSA DT. While the PSA DT after radiation therapy and radical prostatectomy are different in the first 2 years, the rate of increase in PSA appears to be similar in the two groups after year 2, which suggests the rate of growth of cancers that recur after radiation therapy and radical prostatectomy is similar.