Probabilities of benefit and harms of preoperative radiotherapy for rectal cancer: What do radiation oncologists tell and what do patients understand?

•We examine probabilities of benefits/harms mentioned during oncology consultations.•We examine patients’ estimates of these probabilities after the consultation.•Probabilities of harms of treatment often go unmentioned.•Patients often misinterpret the effect of treatment on harms.•Patients tend to underestimate the probabilities of adverse events.

ObjectiveProbabilities of benefits and harms of treatment may help patients when making a treatment decision. This study aimed to examine (1) whether and how radiation oncologists convey probabilities to rectal cancer patients, and (2) patients’ estimates of probabilities of major outcomes of rectal cancer treatment.MethodsFirst consultations of oncologists and patients eligible for preoperative radiotherapy (PRT) (N = 90) were audio taped. Tapes were transcribed verbatim and coded to identify probabilistic information presented. Patients (N = 56) filled in a post-consultation questionnaire on their estimates of probabilities.ResultsProbabilities were mentioned in 99% (local recurrence), 75% (incontinence), 72% and 40% (sexual dysfunction in males and females, respectively) of cases. Most patients (89%) correctly estimated that PRT decreases the probability of local recurrence, and 10% and 38%/54% that it increases the probability of incontinence and sexual dysfunction in males/females, respectively. Patients tended to underestimate the probabilities of harms of treatment.ConclusionOur results show that oncologists almost always mention probabilities of benefit of PRT. In contrast, probabilities of harms often go unmentioned. The effect of PRT on adverse events is often underestimated.Practice implicationsOncologists should stay alert to patients’ possible misunderstanding of probabilistic information and should check patients’ perceptions of probabilities.