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Prostate cancer survival may not correlate with radiation dose in localized disease

A team of researchers from Thomas Jefferson University (PA, USA) have demonstrated that higher doses of radiation may not lead to improved survival when treating localized prostate cancer.

The study, published recently in the American Journal of Clinical Oncology, addresses the previous common assumption that the highest dose of radiation that the body can tolerate will be the most effective at killing cancer.

Senior author Robert Den (Sidney Kimmel Cancer Center, Thomas Jefferson University) commented: “Our results argue that this may not be the case, at least not with lower-risk prostate cancer patients.”

The team performed a meta-analysis on data from 6884 patients, collated from 12 randomized trials of external beam radiation treatment for men with nonmetastatic prostate cancer. Pooling data in this way allowed the authors to demonstrate trends not visible in the individual studies.

Typically, the prostate-specific antigen (PSA) test is used as a measure for patient improvement during radiation therapy. However, within this meta-analysis, the team instead examined long-term markers, such as cancer metastasis or disease-related death.

Findings demonstrated that while PSA levels decreased in line with an increased radiation dose, overall survival, rate of metastasis and other long-term outcome indictors did not improve. These findings thus raise the issue of how we measure treatment outcomes in radiation oncology.

Co-author Adam Dicker (Sidney Kimmel Medical College) commented: “This study suggests that our reliance on the PSA test as a proxy for patient outcomes may not be as useful as many researchers thought, which has broad implications for the design of future clinical trials and the interpretation of current and previous studies.”

Additionally, the study demonstrated that an increased dose is not consistent with increased toxicity levels, indicating that current practices are safe.

Sources: Zaorsky N, Keith S, Shaikh T et al. Impact of Radiation Therapy Dose Escalation on Prostate Cancer Outcomes and Toxicities. American Journal of Clinical Oncology. DOI: 10.1097/COC.0000000000000285 (2016); Thomas Jefferson University press release