Toxicity grade
A 1 to 5 severity scale for side effects: grade 1 mild, grade 2 moderate, grade 3 severe and needing intervention, grade 4 life-threatening, grade 5 fatal. Trials report the percentage of patients with grade 3 or worse.
The Common Terminology Criteria for Adverse Events (CTCAE) define each grade for hundreds of specific effects, from nausea to neutropenia; 'grade 3 or higher' is the usual summary of how hard a treatment is to take, and the rates of dose reduction and discontinuation show how often it cannot be given as planned. Grading is done by clinicians and tends to underestimate symptoms that patients feel but doctors do not see (fatigue, nausea), so patient-reported versions (PRO-CTCAE) are increasingly collected. The same word 'grade' in 'tumour grade' means something entirely different.