Malignancy remains one of the leading causes of mortality worldwide, with global cases projected to exceed 35 million by 2050. Conventional chemotherapeutic agents such as doxorubicin, though effective, are often costly and accompanied by severe toxic effects, underscoring the need for safer, natural, and affordable alternatives. This experimental and quantitative study evaluated the tumoricidal activity of Aratiles (Muntingia calabura L.) leaves ethanolic extract stabilized with chitosan derived from Dalagang Bukid (Caesio cuning) against UVB-induced tumors in Fruit flies (Drosophila melanogaster Meigen). The ethanolic extract was obtained through maceration, while chitosan was isolated from fish scales through deproteinization, demineralization, and deacetylation. Tumor-bearing fruit flies were grouped into 25%, 50%, and 75% extract concentrations, alongside positive (doxorubicin) and negative (distilled water) controls. Data were gathered through microscopic and behavioral observations, focusing on tumor regression, mortality, and overall flies' vitality. Phytochemical screening confirmed the presence of alkaloids, flavonoids, and triterpenoids such as lupenone, compounds known for their tumor-suppressive properties. Results showed that the 50% extract concentration exhibited the highest tumor regression (51.86%), comparable to doxorubicin (54.37%) but with reduced mortality (66.67% vs. 100%). Statistical analysis using one-way ANOVA revealed a significant difference in tumor size reduction (F = 76.12, p < 0.001) but no significant difference in mortality (p = 0.392). These findings suggest that the synergistic effects of lupenone-rich triterpenoids, alkaloids, flavonoids, and chitosan enhanced tumor regression while minimizing toxicity. Overall, the study concludes that Aratiles ethanolic leaf extract with chitosan shows promising potential as a sustainable, safe, and low-cost alternative to conventional chemotherapeutics, meriting further validation in mammalian models for clinical application.