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Background Patients with human papillomavirus–related oropharyngeal cancers have excellent outcomes but experience clinically significant toxicities when treated with standard chemoradiotherapy (70 Gy). We hypothesized that functional imaging could identify patients who could be safely deescalated to 30 Gy of radiotherapy. Methods In 19 patients, pre- and intratreatment dynamic fluorine-18-labeled fluoromisonidazole positron emission tomography (PET) was used to assess tumor hypoxia. Patients without hypoxia at baseline or intratreatment received 30 Gy; patients with persistent hypoxia received 70 Gy. Neck dissection was performed at 4 months in deescalated patients to assess pathologic response. Magnetic resonance imaging (weekly), circulating plasma cell-free DNA, RNA-sequencing, and whole-genome sequencing (WGS) were performed to identify potential molecular determinants of response. Samples from an independent prospective study were obtained to reproduce molecular findings. All statistical tests were 2-sided. Results Fifteen of 19 patients had no hypoxia on baseline PET or resolution on intratreatment PET and were deescalated to 30 Gy. Of these 15 patients, 11 had a pathologic complete response. Two-year locoregional control and overall survival were 94.4% (95% confidence interval = 84.4% to 100%) and 94.7% (95% confidence interval = 85.2% to 100%), respectively. No acute grade 3 radiation–related toxicities were observed. Microenvironmental features on serial imaging correlated better with pathologic response than tumor burden metrics or circulating plasma cell-free DNA. A WGS-based DNA repair defect was associated with response (P = .02) and was reproduced in an independent cohort (P = .03). Conclusions Deescalation of radiotherapy to 30 Gy on the basis of intratreatment hypoxia imaging was feasible, safe, and associated with minimal toxicity. A DNA repair defect identified by WGS was predictive of response. Intratherapy personalization of chemoradiotherapy may facilitate marked deescalation of radiotherapy.

Background Radiation therapy is one of the most commonly used cancer therapeutics, but genetic determinants of clinical benefit are poorly characterized. Pathogenic germline variants in ATM are known to cause ataxia-telangiectasia, a rare hereditary syndrome notable for marked radiosensitivity. In contrast, somatic inactivation of ATM is a common event in a wide variety of cancers, but its clinical actionability remains obscure. Methods We analyzed 20,107 consecutively treated advanced cancer patients who underwent targeted genomic sequencing as part of an institutional genomic profiling initiative and identified 1,085 harboring a somatic or germline ATM mutation, including 357 who received radiotherapy. Outcomes of irradiated tumors harboring ATM loss-of-function (LoF) mutations were compared to those harboring variants of unknown significance (VUS). All statistical tests were two-sided. Results Among 357 pan-cancer patients who received 727 courses of radiotherapy, genetic inactivation of ATM was associated with improved radiotherapeutic efficacy. The 2-year cumulative incidence of irradiated tumor progression was 13.2% vs 27.5% for tumors harboring an ATM LoF vs VUS allele, respectively (HR: 0.51, 95% CI = 0.34-0.77, p= .001). The greatest clinical benefit was seen in tumors harboring bi-allelic ATM inactivation (HR = 0.19, 95% CI = 0.06-0.60, p=.005), with statistically significant benefit also observed in tumors with mono-allelic ATM inactivation (HR = 0.57, 95% CI = 0.35-0.92, p=.02). Notably, ATM LoF was highly predictive of outcome in TP53 wild type tumors, but not among TP53-mutant tumors. Conclusion We demonstrate that somatic ATM inactivation is associated with markedly improved tumor control following radiotherapy. The identification of a radiosensitive tumor phenotype across multiple cancer types offers potential clinical opportunities for genomically-guided radiotherapy.

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