The lack of consistent changes in expression of Class I alleles in human or murine PCa cells suggests that the Class I upregulation and consequent CD8-dependent immune response reported in IGF-depleted or inhibited tumors13,19 may be due not to reduced expression of MHC α-chains, but rather to disruption of peptide transport and processing, and downregulation of invariant Class I component β2M. Here, B2M is linked to posterior cortical atrophy.