UETQuintet at BioCreative IX - MedHopQA: Enhancing Biomedical QA with Selective Multi-hop Reasoning and Contextual Retrieval. - Quoc-An Nguyen; Thi-Minh-Thu Vu; Bich-Dat Nguyen; Dinh-Quang-Minh Tran; Hoang-Quynh Le (CoRR, 2026)