Tongue squamous cell carcinoma (TSCC) is a common oral cancer that has a high propensity for recurrence and metastasis. Therefore, TSCC has a 50% 5-year survival rate. Platinum-based chemotherapy is an effective treatment for squamous cell carcinoma, however, chemotherapy resistance remains a major issue. Therefore, innovative and effective drug combinations are needed to improve TSCC patient prognosis.In this study, we conducted an in vitro CRISPR/Cas9 library screen using two TSCC cell lines (Tscca and Cal27) to identify specific genes that, when inhibited, synergize with cisplatin to effectively suppress tumor growth.We identified STK19 as a potential drug target. Inhibition of STK19 enhances the response of TSCC to cisplatin. Through genetic and pharmacological methods, it has been demonstrated that reducing STK19 activity enhances cisplatin-induced DNA damage. The mechanism involves the depletion of MGMT with STK19 inhibition, leading to conditional lethality and synergistic reduction of tumors in vivo when combined with cisplatin. Overall, in this study, unbiased genetic testing was used to successfully identify synthetic lethal drug combinations for TSCC.STK19 was identified as a promising target that could enhance the killing effects of cisplatin on tongue squamous carcinoma cells, offering a novel therapeutic option for individuals who are insensitive to conventional treatment methods.© 2025. The Author(s).