ASTRO 2018: African-Americans with prostate cancer respond better to radiation therapy than Caucasian men

Contrary to recent data suggesting African-Americans have a higher mortality risk from prostate cancer than Caucasian men, a new study presented Monday, Oct. 22 at the 2018 American Society for Radiation Oncology (ASTRO) Annual Meeting suggests African-American men may have higher cure rates when treated with radiation therapy than Caucasian men.

Recent data suggests African-Americans are two to three-times more likely to die from prostate cancer due to socioeconomic and biological factors, however to the researchers surprise, these study findings suggest race is not independently associated with negative prostate cancer outcomes.   

“When we started this project, we had the commonly-held assumption that African-American men harbor more aggressive disease that leads to lower survival rates,” said lead author Daniel Spratt, MD, an associate professor and chief of the genitourinary radiotherapy program at the University of Michigan Rogel Cancer Center, in Ann Arbor, in a prepared statement. “We were surprised, however, that they appear to be more responsive than Caucasian men to radiation therapy and have improved outcomes following this treatment.” 

For the first part of their study, Spratt and colleagues analyzed gene expression in tumor samples from more than 17,00 men (11.5 percent African-American) with prostate cancer, specifically focusing on androgen receptor activity, sensitivity to radiation and patient outcomes following radiation therapy.  

Tumors from African-American men were found more likely to have low androgen receptor activity, indicating that the tumors were more likely to develop distant metastases within 10 years. However, tumors in the same population also had increased sensitivity to radiation therapy due to differences in gene expression compared to Caucasian men.  

“Differences in gene expression between African-American and Caucasian patients revealed that African-American patients had lower DNA repair and more immunogenic tumors, both of which have been shown to predict better responses to radiation therapy,” Spratt said. 

Secondly, the researchers examined outcomes from 5,854 patients (19.3 percent African-American) in four large randomized prostate cancer trials. In this analysis, African-American men treated with radiation therapy were less likely to experience cancer recurrence or have their cancer spread.  

African-American patients in these trials also had lower rates of biochemical cancer recurrence and distant metastasis, even after controlling for age, performance status, PSA, Gleason grade, T-stage, N-stage and hormone therapy use, according to the researchers.  

Ultimately, study findings demonstrate that racial disparities for prostate cancer are rooted more in societal causes than biology and that patients should be treated irrespective of race, according to Spratt.  

“Our results directly question previously held beliefs from population-based registry data that African-American men independently have worse prostate cancer outcomes than Caucasian men,” he explained. “These findings strengthen the notion that most of the observed disparity found in population datasets regarding stage-for-stage outcomes between African-American and Caucasian men are reflective of social constructs and not rooted in biology.”