A large database analysis showed that the addition of external beam radiotherapy (RT) to androgen deprivation therapy (ADT) significantly improves overall survival (OS) in men with metastatic prostate cancer.
“As advances in systemic therapy for metastatic prostate cancer have improved OS and the control of metastatic disease, a greater interest has emerged in therapies to promote local control of the primary prostatic tumor,” wrote study authors led by Chad G. Rusthoven, MD, of the University of Colorado School of Medicine in Aurora. There is relatively limited data so far, though, on the use of external beam RT in these patients.
The study analyzed outcomes from 6,382 men diagnosed between 2004 and 2012 included in the National Cancer Data Base (NCDB), all of whom received ADT. Of these men, 538 (8.4%) also received prostate RT. The results of the analysis were published in the Journal of Clinical Oncology.
Those who received RT were younger, had better comorbidity scores, lower prostate-specific antigen levels, and higher T stage, and were more likely to have N0 disease, to be treated at a community facility, and to have private insurance.
After a median follow-up of 5.1 years, the addition of RT was associated with a longer median OS of 53 months, compared with 29 months without RT. The 3-year OS rates were 62% with RT and 43% without RT; at 5 years, these rates were 49% and 25%, respectively, and at 8 years, the rates were 33% and 13%.
On a multivariate analysis the effect on survival remained significant, with a hazard ratio of 0.624 (95% CI, 0.551–0.706; P < .001). A propensity score analysis involving 537 RT patients and 537 matched patients who did not receive RT confirmed the result, with improvements in OS rates at multiple time points. A subgroup analysis showed that the biggest benefit of RT was gained in patients with Gleason scores of 8 or below, and for T1–3 tumors compared with T4 tumors. Higher RT dose was also associated with better OS compared with lower doses.
The analysis has limitations inherent to retrospective cohort studies, including the possibility of selection biases and imbalances. The authors noted that performance status and extent of metastatic disease burden could not be controlled for, and the sites of metastatic spread were unavailable.
Still, they concluded, “In this large contemporary analysis, men receiving prostate RT plus ADT lived substantially longer than men treated with ADT alone. Randomized trials to evaluate the impact of local therapy for men with metastatic prostate cancer appear warranted and several trials are ongoing.”