SAN ANTONIO -- Contrary to previous findings, black men who received radiation therapy for prostate cancer had lower rates of biochemical cancer recurrence than white men (HR 0.82, 95% CI 0.74-0.92, P=0.0005) as well as lower rates of distant metastasis (HR 0.70, 95% CI 0.57-0.86, P=0.0008), according to data from randomized RTOG trials reported here by Daniel Spratt, MD, of the University of Michigan in Ann Arbor.
In this app video, Spratt discusses the findings, presented at the American Society for Radiation Oncology meeting, alongside commentators Robert Den, MD, of Thomas Jefferson University, and Neha Vapiwala, MD, of the University of Pennsylvania, both in Philadelphia.
The following is a transcript of their remarks:
Spratt: The first part of this study is looking at a very large prospective registry of over 17,000 tumors, almost 2,000 of which were from black men, looking at the gene expression of their prostate cancers to compare differences between black and white men's tumors. The second part was using individual patient data from randomized trials from RTOG on nearly 6,000 patients with a little over 1,000 African-American men.
What we showed, looking at the biology across the 17,000 patients, is that black patients -- interestingly -- had decreased DNA repair expression as well as increased immune-signaling and inflammatory markers. And when we looked across all the various DNA repair pathways, especially the double-strand break repair pathways -- which are what heal or repair ionizing radiation damage -- these were significantly decreased in black men. In addition, we also showed using a proprietary 24-gene signature that we've developed for prostate cancer, black men appeared to have predicted more radio-sensitive tumors than white men.
And to validate these findings, clinically, what we did is, using that RTOG data, we compared the outcomes of black compared to white men's prostate cancers in regard to biochemical recurrence, distant metastasis, and actually dying from prostate cancer. And although most people believe black patients should have worse outcomes compared to white men, what we actually show is that in the context of a randomized trial, black patients actually have significantly reduced rates of biochemical recurrence, distant metastasis, and actually died less frequently of prostate cancer than white men.
Den: I think what this study really shows us is that we really need to be race agnostic. I think that there has been a prejudice towards being overly-concerned about African-Americans and there were other data that would suggest that actually black men have received less intensive therapy. And I think that is really what's driving the discrepancy in survival that we see in the U.S. population. So it's not actually the biology of their disease; yes, they do present with more aggressive disease, but when you look at other societal influences -- insurance and access to care -- that's where we really see the main drivers that are leading towards an inappropriate, I believe, increased risk of mortality from this disease within the black community.
Vapiwala: Historically, the clinical trial representation from under-represented portions of the population have really been on the order of fewer than 5%. So now to have these kinds of studies in turn reach back out to the community and encourage folks that are in the community to see that not only are the data being used, but that they can be used to benefit the community in turn. And I think [this study is] engendering that trust, and demonstrating that enrollment in a trial is not just something you do and then people kind of forget or neglect or take data from only a certain more majority group and try to apply it to everybody, that something is happening and is happening for the betterment of that population, which will hopefully in turn engender more trust and engender more willingness to participate so those numbers can go even higher.
Spratt: So all these data kind of put together I think question the commonly held notion that population registry data tell us that black patients intrinsically harbor more aggressive disease, and we highlight that they may, in fact, actually do better. Their biology may favor a radiotherapeutic treatment approach.
Primary Source
American Society for Radiation Oncology
Spratt D, et al "Androgen receptor activity and radiotherapeutic sensitivity in African-American men with prostate cancer: A large scale gene expression analysis and meta-analysis of RTOG trials" ASTRO 2018; Abstract 4.