Imatinib for chronic myeloid leukemia
In the IRIS trial, imatinib — a small molecule blocking the BCR-ABL enzyme that drives chronic myeloid leukemia — produced far higher response rates than the previous standard, establishing targeted therapy.
What the study found
IRIS (New England Journal of Medicine, 2003) was a randomized trial comparing imatinib with the previous standard, interferon plus low-dose cytarabine, in newly diagnosed chronic myeloid leukemia (CML). Imatinib is an oral small molecule that blocks BCR-ABL, the abnormal enzyme produced by the "Philadelphia chromosome" that drives CML. Patients taking imatinib had far higher rates of complete cytogenetic response — the disappearance of the Philadelphia chromosome — and were much more likely to stay progression-free, with fewer serious side effects than the older regimen.
Why it matters
CML had been a disease with limited options and poor long-term outcomes. Imatinib targeted the specific molecular fault causing the cancer, rather than broadly poisoning dividing cells the way chemotherapy does. It turned a frequently fatal leukemia into, for many patients, a long-term manageable condition, and became the proof of concept that a drug aimed at a defined driver mutation could transform a cancer's course.
Analysis — the pattern
This sits at the root of a broad pattern (analysis, not a single-study claim): sequencing a tumor for actionable drivers and matching a targeted inhibitor now runs through much of oncology, from EGFR in lung cancer to HER2 in breast cancer. A recurring limit is resistance — cancers evolve new mutations that evade the drug — which drove development of later-generation inhibitors.
What is still uncertain
Not every cancer has a single clean driver like BCR-ABL, and resistance, the question of whether some patients can safely stop therapy, and long-term effects of indefinite treatment remain active areas of study.