Despite important technological innovations to allow more accurate and precise targeting for external-beam radiotherapy, such as intensity modulated radiation therapy (IMRT), and better consideration of patient and tumor characteristics, radiation oncology still has not yet developed tools analogous to HER2/neu testing to identify breast tumors that might respond to the targeted agent trastuzumab (Herceptin).1 But that might be changing.

Most cancer patients undergo radiation therapy but efforts to personalize radiation oncology have lagged behind advances in other treatment modalities, such as anticancer agents that target specific tumor mutation-affected gene pathways.

Intensity modulated radiation therapy and other beam targeting technologies, and advances in planning algorithms and imaging, represent important advances in more precisely delivering radiation to tumors while sparing healthy nontarget tissues.1 These advances are expected to improve tumor responses and reduce patient toxicity risks. But the therapeutic ratio could be improved further still if molecular tools were available for predicting patient and tumor radiosensitivities.1-4 Knowing tissue radiosensitivities in the target volume and candidate beam pathways would allow treatment planning that is better tailored to a particular patient’s biology and tumor biology. Tumor and nontumor cell genotypes can influence responses to radiation, affecting tumor-control efficacy and radiotoxicities.

Predicting intrinsic radiosensitivities has therefore been called the Holy Grail of radiobiology.2

“Despite its common use in cancer treatment, radiotherapy has not yet entered the era of precision medicine, and there have been no approaches to adjust dose based on biological differences between or within tumors,” wrote Javier F. Torres-Roca, MD, of the Moffitt Cancer Center and Research Institute, Tampa, Florida.3

That partly reflects scarce funding; less than 2% of federal health research money goes to radiation oncology.1

But Torres-Roca and colleagues’ findings suggest a new path toward part of radiation therapy’s Holy Grail: predicting tumor radiosensitivity.3