Search

Purpose Understanding prostate-specific antigen (PSA) kinetics after radiation therapy plays a large role in the management of patients with prostate cancer (PCa). This is particularly true in establishing expectations regarding PSA nadir (nPSA) and PSA bounces, which can be disconcerting. As increasingly more patients are being treated with stereotactic body radiation therapy (SBRT) for low- and intermediate-risk PCa, it is imperative to understand the PSA response to SBRT. Methods and Materials PSA data from 5 institutions were retrospectively analyzed for patients with localized PCa treated definitively with SBRT alone from 2004 to 2016. Patients received 35 to 40 Gy in 5 fractions, per institutional standards. Patients who had less than 12 months of PSA data or received androgen deprivation therapy were excluded from this study. Linear and logistic multivariable analysis were performed to identify predictors of nPSA, bounce, and biochemical recurrence, and joint latent class models were developed to identify significant predictors of time to biochemical failure. Results A total of 1062 patients were included in this study. Median follow-up was 66 months (interquartile range [IQR], 36.4-89.9 months). Biochemical failure per the Phoenix criteria occurred in 4% of patients. Median nPSA was 0.2 ng/mL, median time to nPSA was 40 months, 84% of patients had an nPSA ≤0.5 ng/mL, and 54% of patients had an nPSA ≤0.2 ng/mL. On multivariable analysis, nPSA was a significant predictor of biochemical failure. Benign PSA bounce was noted in 26% of patients. The median magnitude of PSA bounce was 0.52 ng/mL (IQR, 0.3-1.0 ng/mL). Median time to PSA bounce was 18.1 months (IQR, 12.0-31.1 months). On multivariable analysis, age and radiation dose were significantly associated with a lower incidence of bounce. Joint latent class models modeling found that nPSA and radiation dose were significantly associated with longer time to biochemical failure. Conclusions In this multi-institutional cohort of patients with long-term follow-up, we found that SBRT led to low nPSAs. In turn, lower nPSAs are associated with reduced incidence of, and longer time to, biochemical failure. Benign PSA bounces occurred in a quarter of patients, as late as several years after treatment. Further studies are needed to directly compare the PSA response of patients who receive SBRT versus other treatment modalities.

PURPOSE/OBJECTIVE(S) There is a lack of early predictive measures of outcome for patients with intermediate-risk prostate cancer (PCa) treated with stereotactic body radiotherapy (SBRT). We aim to explore 4-year PSA response rate (4yPSARR) as an early predictive measure. MATERIALS/METHODS Individual patient data from 6 institutions for patients with intermediate-risk PCa treated with SBRT between 2006 and 2016 with a 4-year (42-54 months) PSA available were analyzed. Cumulative incidences of biochemical failure and metastasis were calculated using Nelson-Aalen estimates and overall survival was calculated using the Kaplan-Meier method. Biochemical failure-free survival was analyzed according to 4yPSARR with groups dichotomized based on PSA < 0.4 ng/mL or ≥ 0.4 ng/mL and compared using the log-rank test. Multivariable competing risk analysis was performed to predict for biochemical failure and development of metastasis. RESULTS Six-hundred thirty-seven patients were included, including 424 (67%) with favorable and 213 (33%) with unfavorable intermediate-risk disease. Median follow-up was 6.2 years (IQR 4.9-7.9). The cumulative incidence of biochemical failure and metastasis, and overall survival at 6 years was 7%, 0.6% and 97%, respectively. The cumulative incidence of biochemical failure at 6 years if 4yPSARR < 0.4ng/mL was 1.7%, compared to 27% if 4yPSARR ≥ 0.4 ng/mL (P < 0.0001). On multivariable competing risk analysis, 4yPSARR was a statistically significant predictor of biochemical failure-free survival (sHR 15.3, 95% CI 7.5-31.3, P < 0.001) and metastasis-free survival (sHR 31.2, 95% CI 3.1-311.6, P = 0.003). CONCLUSION 4yPSARR is an encouraging early predictor of outcome in patients with intermediate-risk PCa treated with SBRT. Validation in prospective trials is warranted.

PURPOSE/OBJECTIVE(S) Stereotactic body radiation therapy (SBRT) has emerged as a promising modality for the treatment of prostate cancer (PCa) and involves the delivery of ablative doses of radiation to the prostate. The patterns of failure at the time of biochemical recurrence (BCR) after SBRT remain unknown. The purpose of this study is to explore the development of distant metastasis (DM) following the diagnosis of BCR. MATERIALS/METHODS We queried a multi-institutional database of 2,430 patients who were prospectively treated with SBRT on single institution phase II trials or registries to identify patients who developed a BCR by the Phoenix criteria or by initiation of salvage therapy for PSA rise at a lower threshold. Patterns of distant failure were obtained for patients who had BCR, including presence and sites of DM. Multivariable analysis (MVA) using logistic regression was used to evaluate the association between multiple clinicopathologic and treatment variables and DM. RESULTS 150 patients with BCR were identified (6.2% of total). Of these, 19% presented with low-risk, 42% with intermediate-risk, and 39% with high-risk disease. The median PSA at BCR was 4.56, median time to BCR was 36 months, and median follow-up after BCR was 15.5 months. Sixty-seven patients (44.7%) had DM identified at or after the time of BCR. Among those with DM, 13 had M1a disease, 50 had M1b disease, 3 had M1c disease, and 1 had an unknown distribution of disease. Time to BCR was significantly shorter in patients with DM compared to those who did not have DM (28.1 vs. 41.4 months, P = 0.002) and initial PSA (iPSA) was significantly greater (11.0 vs. 8.0, P = 0.03). On MVA, Gleason Grade Group (GG) 4 (vs. GG 1, OR 3.76, P = 0.047) and higher SBRT dose (36.25 Gy vs. 35 Gy: OR 4.03, P = 0.02; 40 Gy vs. 35 Gy: OR 3.73, P = 0.03) were significantly associated with DM. CONCLUSION A substantial proportion of patients with BCR after SBRT for localized PCa ultimately develop DM, particularly those with higher iPSA and shorter time to BCR. The association with SBRT dose is likely reflective of the use of higher doses in more modern cohorts with higher-risk disease, while the association with GG likely reflects the more aggressive biology of these tumors at presentation. Further research into patterns of failure after SBRT is needed, especially in the context of more sensitive nuclear imaging. Early predictors of treatment failure are needed to facilitate timely treatment intensification.