What is this summary about?This is a summary describing the results from CHAPTER-GIST-301 a phase 3 clinical study evaluating a new drug therapy called pimitespib in people who have been diagnosed with advanced gastrointestinal stromal tumor (GIST).GIST is a rare type of cancer found in the wall of the digestive system (the gastrointestinal tract). The people enrolled onto this study had already tried and failed treatment with the standard first-, second- and third-line tyrosine kinase inhibitor (TKI) therapies for GIST and were in need of a fourth-line treatment option.The aims of the study were to look at how well pimitespib worked compared with a placebo (a treatment with no active ingredient) and also to understand what side effects resulted from using pimitespib.What were the results?The results of the CHAPTER-GIST-301 study showed that pimitespib significantly increased the length of time that people survived without their cancer getting worse (progression-free survival) and the length of time that people survived overall (cross-over-adjusted overall survival). Pimitespib was generally well tolerated, and safety was manageable with dose adjustments when needed.What do the results mean?Pimitespib was proven to have favorable safety and significantly increased the length of time that people survived without their cancer getting worse and how long they survived overall. The results of the CHAPTER-GIST-301 study led to pimitespib, also known by the brand name JESELHY®, being approved in Japan in 2022 for people with advanced GIST that has progressed after treatment with standard first-, second- and third-line TKIs, imatinib, sunitinib and regorafenib.[Box: see text].