ANPEP and metastatic malignant neoplasm: The observation that MHC-I expression is reduced in A9 metastatic cell lines compared to TC1 primary cell lines (Schnare et al., 2001; Jones and Baylin, 2002; Reiman et al., 2007) (Figure 1) points to loss of expression of MHC-I and other APM components as a mechanism of immune evasion by metastatic cancer.