The advent of affordable and rapid next-generation DNA sequencing technology, along with the US Supreme Court ruling invalidating gene patents, has led to a deluge of germline and tumor genetic variant tests that are being rapidly incorporated into clinical cancer decision making. A major concern for clinicians is whether the presence of germline mutations may increase the risk of radiation toxicity or secondary malignancies. Since minimal clinical data exist to inform decisions at this time, the American Society for Radiation Oncology (ASTRO) convened a group of radiation science experts and clinicians to summarize potential issues, review relevant data, and provide guidance for adult patients and their care teams regarding the impact, if any, that genetic testing should have on radiation therapy recommendations.

During the ASTRO Workshop, several main points emerged, which are discussed in this manuscript: 1) Variants of uncertain significance should be considered non-deleterious until functional genomic data emerges to demonstrate otherwise; 2) Possession of germline alterations in a single copy of a gene critical for radiation damage responses does not necessarily equate to increased risk of radiation-induced toxicity; 3) Deleterious ATM mutations may modestly increase second cancer risk after radiotherapy, thus follow-up for these patients after indicated radiotherapy should include second cancer screening; 4) Conveying to patients the difference between relative and absolute risk is critical to decision making; and 5) More work is needed to assess the impact of tumor somatic alterations on the probability of response to radiotherapy and the potential for individualization of radiation doses. Data on radiosensitivity related to specific genetic mutations is also briefly discussed.