Side effect versus adverse event

Counting every adverse event, including those from the cancer itself or from unrelated illness, is deliberate: it avoids under-reporting and lets the two arms be compared fairly, since the control arm has adverse events too. Investigators then attribute each event as related or unrelated to treatment, yielding 'treatment-related adverse events', and grade its severity; drug labels list the side effects seen more often on the drug than on placebo. Some harms appear only years later (heart damage from anthracyclines, second cancers after radiation, permanent hormone deficiencies after immunotherapy) and are called late effects, and survivorship care exists to watch for them.