Identification of STK35L1 as a potential prognostic biomarker in breast carcinoma, and its expression exhibits high correlation with EGFR activity.

Breast cancer (BC) is the second most prevalent malignancy after lung cancer, and the life expectancy is still very low due to therapeutic resistance and tumor relapse. It is crucial to identify novel biomarkers that can serve as potential therapeutic targets. In TNBC, aberrant activation of EGFR has also been implicated in the development of drug resistance. STK35L1 is a critical regulator of diverse cellular processes, including apoptosis and DNA damage. Notably, STK35L1 promotes drug resistance and regulates glycolysis and apoptosis through AKT signaling. The oncogenic role of STK35L1 is established in various cancers, including osteosarcoma, colorectal cancer, and acute myeloid leukemia. However, its association in BC has not yet been explored. In this study, we found that STK35L1 was significantly upregulated in multiple cancers, and its higher expression was associated with poor survival outcomes in BC patients. STK35L1 was differentially upregulated across all BC subtypes. An association between EGFR and STK35L1 expression was observed in normal breast tissues but not in BC. Interestingly, compared with normal breast tissue, EGFR mRNA expression is downregulated in BC tissues, with the greatest downregulation in the luminal B subtype and the least in TNBC. Furthermore, EGFR inhibition with gefitinib increased STAT3 phosphorylation at Tyr-705, and STK35L1 and EGFR gene expression were significantly upregulated. These data suggest that EGFR-STAT3 signaling may regulate STK35L1 and EGFR expression. In conclusion, we report an association of STK35L1 and EGFR in BC, highlighting STK35L1 as a potential prognostic biomarker and therapeutic target.