The following article features coverage from the American Society of Clinical Oncology 2020 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Adjuvant imatinib for 36 months following complete resection of gastrointestinal stromal tumor (GIST) prolonged overall survival (OS) and recurrence-free survival (RFS) compared with 12 months of adjuvant imatinib, according to results from nearly 10 years of follow-up presented during the ASCO20 Virtual Scientific Program.

During his presentation, Peter Reichardt, MD, PhD, of the Helios Klinkikum Berlin-Buch in Germany, explained that “overall, about 50% of deaths can be avoided during the first 10 years of follow-up after surgery with the longer adjuvant imatinib treatment.”

In the Scandinavian Sarcoma Group (SSG) XVIII/German AIO trial, OS was longer after 36 months of adjuvant imatinib with both 54 and 90 months of follow-up. This open-label, multicenter, phase 3 trial evaluated efficacy and safety after nearly 10 years of follow-up.

Researchers randomly assigned 400 adult patients with GIST who underwent macroscopic surgery and who were deemed high risk for recurrence with 400 mg/day of imatinib for either 12 months or 36 months. The primary endpoint was RFS and the secondary endpoints included OS and safety.


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At baseline, the median patient age was 61 and 50.5% of patients were male. The median tumor size was 9.5 cm, the median mitosis count was 9/50 high power fields, and tumor rupture occurred in a mean of 20% of patients.

During a median follow-up of 9.9 years, RFS was significantly longer with 36 months versus 12 months of imatinib. In the intention-to-treat (ITT) population, the 5-year RFS was 71.4% with 36 months of imatinib compared with 53.0% with 12 months of imatinib. The 10-year RFS was 52.5% and 41.8%, respectively (hazard ratio [HR], 0.66; 95% CI, 0.49-0.87; P =.003).

OS was also significantly prolonged with 36 months of imatinib, with a 5-year rate of 92.0% compared with 86% with 12 months of imatinib. The 10-year OS was 79.0% and 65.3%, respectively (HR, 0.55; 95% CI, 0.37-0.83; P =.004).

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In the subgroup analysis, “most importantly, favoring the 3-year group, patients with a local mitotic count of >10, central mitotic count of >10, and KIT exon 11 mutation,” said Dr Reichardt.

The results were similar in the efficacy population of 358 patients, which excluded patients who were misdiagnosed with GIST and patients who had intra-abdominal metastases removed at the time of surgery. In this population, the 10-year OS was 81.6% in patients who received 36 months of imatinib compared with 66.8% in those who received 12 months of imatinib (HR, 0.50; 95% CI, 0.32-0.80; P =.003).

There were no new safety signals in either treatment group.

Dr Reichardt concluded that “3 years of adjuvant imatinib is highly superior in efficacy with respect to RFS and, most importantly, OS as compared to 1 year of imatinib.”

Read more of Cancer Therapy Advisor‘s coverage of the ASCO 2020 meeting by visiting the conference page.

Reference

Joensuu H, Eriksson M, Hall KS, et al. Three versus one year of adjuvant imatinib for high-risk gastrointestinal stromal tumor (GIST): Survival analysis of a randomized trial after 10 years of follow-up. Presented at: ASCO20 Virtual Scientific Program. J Clin Oncol. 2020;38(suppl):abstr 11503.