Hyperbaric oxygen therapy (HBOT) represents a modality of interest to many oncologists, even if not well understood and seldom used by many in practice. To the radiation oncologist in particular, and to patients who experience late toxicities of radiotherapy such as fibrosis and pain, HBOT offers an ember of hope in the desperate attempt to treat these chronic adverse effects of therapy. The US Food and Drug Administration has cleared HBOT for marketing in the framework of regulated medical devices for several conditions, such as nonhealing wounds, decompression sickness, and radiation injury. 1 Work is also ongoing to determine efficacy of HBOT in diverse scenarios ranging from a priori radiation sensitization to chronic fatigue syndrome and from early use to use only in desperate situations. 2 However, the agency cautions clinicians to be wary of unproven claims of effect, perhaps highlighting the vulnerability of patients seeking therapy for some of the most troubling ailments. Moreover, there is concern that the burgeoning industry of HBOT might include unscrupulous centers since only 154 facilities in the United States, out of well over 1000, are accredited by the Undersea and Hyperbaric Medical Society, 3 and findings of misuse have been previously documented. 4 In JAMA Oncology, Mink van der Molen et al 5 report results of the Effect of Hyperbaric Oxygen Therapy on Breast Cancer Patients With Late Radiation Toxicity (HONEY) trial, generating the best evidence to date for prescribing HBOT to treat late toxicities of breast radiotherapy. The authors use a creative study design, drawing from a larger cohort of patients with breast cancer who have already consented to prospective quality of life data collection. 6 This cohort had previously provided additional consent to partake in randomized trials of unknown future interventions, with further consent required for particular interventions if randomized to the experimental arm. However, if randomized to the control arm, patients were neither informed nor was their further consent required, and their data served as the control. Within this structure, the HONEY investigators identified patients treated for breast cancer at least 12 months after radiotherapy who reported moderate/severe breast, chest wall, and/or shoulder pain in combination with at least 1 symptom of mild/moderate/severe fibrosis, breast edema, and/or movement restriction, based on questionnaire responses. The intervention was an invitation to HBOT, in which patients breathed 100% oxygen during 4 intervals of 20 minutes in a 2-hour session, for 30 to 40 sessions, spanning 6 to 8 weeks. Patients were categorized as HBOT adherent if they participated in treatment and categorized as HBOT nonadherent if they attended less than 7 sessions or declined treatment.