HSP90AA1 and neoplasm: Extracellular Hsp90 displays non-canonical functions, as illustrated by its being expressed on the surface of tumor cells surface (Altmeyer et al. 1996) while chaperoning tumor peptides and presenting them to MHC class I molecules of antigen-presenting cells (APCs), a process known as “cross presentation” (Lammert et al. 1997; Spee and Neefjes 1997; Evdokimovskaya et al. 2012).