The plant kingdom serves as a valuable resource for cancer drug development. This study explored the antitumor activity of different sub-fractions (hexane, dichloromethane and methanol) of (gorse) methanol extract in glioblastoma (U-87MG and U-373MG) and neuroblastoma (SH-SY5Y) cell lines, along with their phytochemical profiles. Cytotoxicity was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays, and cell cycle arrest and apoptosis were assessed through flow cytometry and by measuring reactive oxygen species (ROS) and protein expression levels. D7 and D8 dichloromethane sub-fractions significantly reduced cell viability, triggered early apoptosis in SH-SY5Y and U-87MG cells and specifically increased ROS levels in U-87MG cells. Western blot analyses showed that D7 increased p53, caspase-3, caspase-8 and γH2AX expression in SH-SY5Y and U-87MG cells, while D8 specifically elevated p53 in SH-SY5Y cells and caspase-3 in both cell lines. In U-373 cells, D7 and D8 markedly reduced cell viability, with D8 inducing necrosis. Morphological changes indicative of apoptosis were also observed in all cell lines. Bioinformatic analysis of UHPLC-MS and GC-MS data tentatively identified 20 metabolites in D7 and 15 in D8, primarily flavonoids. HPLC-DAD confirmed isoprunetin and genistein as the most abundant in D7 and D8, respectively, both isolated and identified by NMR spectroscopy. Most of the flavonoids identified have been reported as antitumor agents, suggesting that these compounds may be responsible for the observed pharmacological activity.