Hepatocellular carcinoma (HCC) accounts for 90% of primary liver cancers and is the third leading cause of cancer-related deaths globally (Daniel Q et al., 2023). In China, HCC has the lowest survival rate among all cancers, with a 5-year relative survival rate of only 10.1% (Diyang et al., 2022). For early - stage HCC, treatment is whole/partial liver resection or transplantation. Intermediate - stage patients get local therapies like transarterial chemoembolization. But over 50% of patients have advanced HCC at diagnosis due to late - onset symptoms, requiring systemic treatment (Chen et al., 2022). For advanced HCC patients, chemotherapy is the core of systemic treatment. However, tumor - specific resistance, high malignancy, local recurrence, and distant metastasis cause severe side - effects and drug resistance, leading to poor treatment results and harm to patients (Xupeng et al., 2024). Finding new HCC treatment drugs remains important. Since new drug development demands a lot of resources, repurposing existing clinical drugs is now a research focus.

Erythromycin, a macrolide antibiotic, binds to the 50S ribosomal subunit in bacterial cells. It inhibits different phases of bacterial protein synthesis, suppressing protein production to have antimicrobial effects. Clinically, it's mainly used for treating streptococcal tonsillitis, scarlet fever, diphtheria (including carriers), gonorrhea, listeriosis, and lower respiratory tract infections by Streptococcus pneumoniae (Elinor et al., 2021; Maxim S et al., 2021). Studies have shown that macrolide compounds can inhibit cancer cell proliferation by modulating various targets and signaling pathways. For instance, rapamycin and azithromycin can not only block mTOR function, exhibiting anti-proliferative activity in multiple malignancies, but also reduce the expression of vascular endothelial growth factor (VEGF) in tumor tissues, inhibiting tumor development (Naoharu et al., 2023; Yuji et al., 2024). Erythromycin, as a leading macrolide antibiotic, has also been found to possess certain anti-tumor properties (Keisuke et al., 2023). However, its anti - hepatocellular carcinoma mechanisms and anti - tumor effects need further exploration.

CD24 (Cluster of Differentiation 24) is a highly glycosylated glycosylphosphatidylinositol-anchored surface protein overexpressed in nearly all tumor cells. It regulates cell migration, invasion, and proliferation, and is involved in cell adhesion and tumor metastasis. CD24 expression is strongly linked to poor prognosis in cancer patients and serves as a diagnostic marker for tumor and neuroendocrine differentiation (Jie et al., 2024; Kun et al., 2023). Studies have revealed that CD24 expressed on the surface of tumor cells is recognized as a macrophage phagocytosis-inhibitory molecule (a "don't eat me" signal) (Weijian et al., 2023). When CD24 binds to Siglec-10 on the macrophage, it triggers an inhibitory signaling cascade mediated by protein tyrosine phosphatases such as SHP-1 or SHP-2 with Src homology 2 domains. Siglec-10 recruits and activates proteins containing SH2 domains, particularly SHP-1, SHP-2, and Suppressor of Cytokine Signaling 3 (SOCS3), reducing inflammation from damage-related molecular patterns (Amira A et al., 2019). Moreover, the binding of CD24 to Siglec-10 also blocks Toll-like receptor-mediated inflammatory responses, allowing tumor cells to evade macrophage surveillance and clearance, promoting immune escape, and accelerating tumor progression (Yu'e et al., 2023). Therefore, developing drugs that block the CD24 pathway is an effective strategy for cancer treatment. This paper shows that erythromycin can cut CD24 on tumor cell surfaces and has anti - hepatocellular carcinoma effects, giving evidence for using erythromycin as a new clinical treatment target.