What is this summary about?This is a summary of the DeFi study, published in The New England Journal of Medicine in March 2023. In the DeFi study, researchers were studying if the drug called nirogacestat (Ogsiveo®) could slow disease progression and improve disease symptoms. The study included 142 adults with progressing desmoid tumors.In summary, what were the DeFi study results?In this study, researchers found that: Nirogacestat reduced the chance of a participant’s disease getting worse during the study by 71% compared with a placebo.41% of the participants had their tumors respond to treatment with nirogacestat. 7% of the participants had their tumors disappear completely and 34% of the participants had their tumors shrink by at least 30% during the study.Participants who took nirogacestat had significant reduction of pain and disease-related symptoms, improvement in their ability to perform daily activities, and improvement in their overall quality of life compared with participants who took a placebo.Almost all participants who took nirogacestat had side effects, and most side effects were mild or moderate.Among participants who received nirogacestat, the most common side effects were diarrhea, nausea, fatigue, low levels of phosphate in the blood (hypophosphatemia), and rash.75% of women expected to be able to have children who took nirogacestat had ovarian toxicity. Ovarian toxicity was identified and reported by researchers based on abnormal blood hormone levels or symptoms associated with the onset of menopause, such as missed menstrual periods. Among women who had ovarian toxicity, researchers reported that 74% had their ovarian toxicity resolve, including in 100% of those women who stopped taking nirogacestat for any reason. –4 participants stopped treatment with nirogacestat due to ovarian toxicityWhat do the results mean?Nirogacestat helped to shrink desmoid tumors, decrease pain, decrease the severity of symptoms related to desmoid tumors, improve the ability to perform daily activities, and helped improve overall quality of life in participants more than a placebo. Participants taking nirogacestat experienced more side effects than participants taking a placebo.[Box: see text].