Most patients in the United States who receive stereotactic body radiation therapy (SBRT) for unfavorable intermediate- or high-risk localized prostate cancer are not receiving concurrent androgen-deprivation therapy (ADT), despite national guideline recommendations that support the concurrent use of ADT with radiation therapy.
Among patients aged >40 years with localized prostate cancer who received radiation therapy between 2004 and 2015, the use of ADT decreased among those who were considered low risk, favorable intermediate risk, or unfavorable intermediate risk, according to an analysis of data from the National Cancer Database. The use of ADT increased over time only among men with high-risk disease, reported Trevor J. Royce, MD, MPH, MS, Assistant Professor, Department of Radiation Oncology, University of North Carolina at Chapel Hill, and colleagues, in a poster presentation at the 2020 Genitourinary Cancers Symposium.
“In general, because there is the potential for quality-of-life effects from ADT, best practice is to use it when there is a proven benefit,” noted Dr Royce and colleagues. “To be clear, ADT is an extraordinarily effective approach for treating prostate cancer, it’s just that as clinicians we aim to be judicious with its application.”
Randomized clinical trials have demonstrated an improvement in survival with the addition of ADT to conventionally fractionated radiotherapy for men with unfavorable intermediate-risk or high-risk localized prostate cancer. As a result, guidelines from the National Comprehensive Cancer Network recommend the use of ADT with radiation therapy in patients with unfavorable intermediate-risk or high-risk disease.
Although SBRT is noninferior to conventional radiation for tumor control and toxicity, and noninferior to moderate hypofractionation for toxicity, the benefit of ADT combined with SBRT is unknown.
Using the National Cancer Database, the investigators identified men aged >40 years with localized prostate cancer who received radiation (excluding brachytherapy) between 2004 and 2015. ADT prescribed for ≤180 days of radiation was considered combined modality therapy. SBRT was defined as ≥5 Gy per fraction. Non-SBRT external beam radiation therapy (EBRT) was defined as ≤3 Gy per fraction and a total dose ≥60 Gy per fraction. Of the 141,384 men included in the study, 7599 received SBRT and 133,825 received EBRT.
The use of SBRT increased significantly for all risk groups from 2004 to 2015, from 0.9% to 10.3% (P <.001). Specifically, SBRT use increased from 0.9% to 21.6% in the low-risk group, from 1.1% to 13.7% in the favorable intermediate-risk group, from 0.6% to 10.8% in the unfavorable intermediate-risk group, and from 0.8% to 2.8% in the high-risk group.
During the same time period, the use of ADT decreased among all patients, from 60.8% to 39.2% (P <.001). Specifically, ADT use decreased from 22.8% to 5.5% in the low-risk group, from 51.7% to 40.0% in the favorable intermediate-risk group, and from 53.4% to 49.5% in the unfavorable intermediate-risk group. The only group for which an increase in the use of ADT was reported was the high-risk group, where use of this modality increased from 78.9% to 84.2%.
Across all risk groups, the likelihood of receiving ADT was higher in men who received EBRT than in men who received SBRT. Overall, the use of ADT was 49.2% among men who received EBRT and 15.4% among those who received SBRT. When stratified by risk group, the use of ADT among men who received EBRT compared with SBRT was 13.1% versus 5.0% in the low-risk group, 42.7% versus 14.9% in the favorable intermediate-risk group, 48.2% versus 19.2% in the unfavorable intermediate-risk group, and 81.2% versus 41.5% in the high-risk group, respectively.
On multivariable analysis, the use of ADT was significantly less likely among men who received SBRT versus men who received EBRT across all risk groups (P <.001).
“ADT use has likely decreased over time because we have a greater appreciation for its quality of life effects, and because prostate cancer risk stratification has improved and we have a better sense of who stands to receive the most benefit with ADT,” the researchers concluded.