PLAC1 and head and neck squamous cell carcinoma: In C3H/HeJ mice, Plac1‐OE cells formed larger tumors (p = 0.0003) and weighed more (p = 0.0115) than tumors derived from Plac1‐NC cells (Figure 5F,G) and we found that the tumor‐promoting effects were more significant in immune‐competent mice than those in immunodeficient mice (Balb/c nude: p = 0.0024, C3H/HeJ: p = 0.0003) (Figure S9G, Supporting Information), which indicated that the Plac1‐related immune microenvironment was crucial during HNSCC progression.