The ASCENDE-RT randomized clinical trial demonstrated that the combination of external beam radiation with a brachytherapy boost (EBRT+BT) significantly reduced biochemical progression-free survival. A new data analysis suggests that the benefit may extend to prostate cancer survival as well.
Xiang and Nguyen searched the SEER database to identify 52,535 high- and intermediate-risk patients who were treated with EBRT+BT or EBRT alone in 2004-2011. Of that total, 20% received EBRT+BT, and one-third were high risk. They matched patients for risk factors, and adjusted for other variables that affect survival. By 8 years after treatment, the adjusted prostate cancer-specific mortality was:
- · 1.8% for EBRT+BT
- · 2.7% for EBRT
- · 5.4% for EBRT+BT among high-risk patients
- · 7.6% for EBRT among high-risk patients
- · Mortality was not significantly reduced among intermediate-risk patients
The authors conclude:
“BT boost was associated with a moderate reduction to PCSM in men with localized unfavorable-risk prostate cancer. Those most likely to benefit are younger patients with high-risk disease.”
Of course, this was a database analysis and not a randomized clinical trial, so the findings are provisional until better data are available. The mortality numbers are small, reflecting the long natural history of prostate cancer progression even among high risk patients, and the fact that at modern dose levels, both the monotherapy and the combined modality may cure or delay progression for a long time. As we’ve seen, the combined modality approach does increase the side effects of treatment. The fact that there is so far no discernable survival benefit for intermediate risk patients, should dissuade those with “favorable intermediate risk” prostate cancer from pursuing boost therapy. Each unfavorable risk patient will have to assess for himself whether the added toxicity is worthwhile.