Efficacy and Objective Response of MEK Inhibitors in Rare Cancers: A Systematic Review and Meta-analysis of Randomized Clinical Trials

Background: Rare digestive system cancers, including cholangiocarcinoma and other low-incidence malignancies, have limited treatment options and often harbor alterations in the RAS-RAF-MEK-ERK pathway.MEK inhibitors have shown preclinical activity, but clinical efficacy remains unclear.This systematic review and meta-analysis evaluated the therapeutic impact of MEK inhibitors in rare digestive cancers.Methods: Following PRISMA guidelines, MEDLINE, Cochrane Library, and ClinicalTrials.gov were searched for randomized phase II or III trials investigating MEK inhibitors in rare cancers.Data extraction and riskof-bias assessment were performed independently by two reviewers.Pooled odds ratios (OR) were calculated using randomor fixed-effects models depending on heterogeneity.Results: Total of 522 records screened, four phase II trials (n=210) met inclusion criteria, evaluating selumetinib, trametinib, and cobimetinib.MEK inhibitor therapy did not improve ORR compared with control (OR 0.93; 95% CI 0.35-2.48;I 2 =0%).No complete responses were reported.Most studies demonstrated high performance and detection bias due to open-label design, and overall certainty of evidence was rated low.Conclusions: MEK inhibitors showed limited clinical activity in rare digestive system cancers and the current evidence remains insufficient to confirm their efficacy as either monotherapy or in combination therapy.Future trials should incorporate biomarker-selected populations and rational combination strategies to overcome pathway resistance.