TLR4 and basal cell carcinoma: Currently, there are three TLRs agonists, BCG (TLR2/TLR4 agonist) [19], imiquimod (R-837) (TLR7 agonist) [20], and monophospholipid A (MPLA) (TLR4 agonist) [21] approved for bladder cancer, basal cell carcinoma, and vaccine adjuvant, respectively.