A comprehensive pooled analysis of data from 17 SWOG Cancer Research Network phase 2 and 3 clinical trials, spanning from 1990 to 2022, has revealed a strong association between a patient's self-reported fatigue levels prior to beginning cancer treatment and the subsequent risk of severe adverse events (AEs). Published in *JAMA Oncology*, the study included 7,086 patients with various cancer types such as prostate, lung, colorectal, lymphoma, breast, melanoma, ovarian, and pancreatic cancer. The findings indicate that patients reporting at least some baseline fatigue were significantly more likely to experience severe (grade 3 or worse), life-threatening (grade 4 or worse), or fatal (grade 5) toxic effects during therapy. Specifically, those with any baseline fatigue had approximately twice the risk of severe or worse toxic effects compared to those with no or minimal fatigue. Furthermore, patients reporting 'quite a lot' or 'very much' fatigue at baseline faced an almost fivefold higher risk of fatal toxic effects. This research, led by Joseph Unger and colleagues from Fred Hutchinson Cancer Center, highlights that baseline fatigue assessments can serve as an early clinical marker to predict the risk of treatment-related toxicities. The observed dose-response relationship, where the likelihood of AEs increased with escalating fatigue levels, provides compelling evidence for integrating fatigue assessment into personalized treatment planning and symptom monitoring. Understanding this link can potentially lead to adjusted care plans, closer monitoring, or tailored interventions to mitigate debilitating side effects, ultimately improving patient outcomes.