The features making MSLN an ideal immunotherapeutic target in MM are: A) the high level of MSLN expression in cancer tissue and low-to-no expression in healthy tissue, thus reducing possible ‘on target/off-tumor’ toxicities [11]; B) 85–90% of cases in the epithelioid subtype of MM present with high expression of MSLN [12]; and C), its expression at high levels has been associated with increased aggressiveness and invasiveness [13]. This evidence concerns the gene MSLN and cancer.