IGHE and neoplasm: However, since CD38 expression on MM cells is higher compared to most normal cells, CD38 is considered to be a tumor-associated antigen [42,43,44,64], combined with the fact that the MM is infiltrated by IgE effector cells including mast cells [45,46,52,53], suggests that the type I hypersensitivity reaction would be preferentially localized in the tumor microenvironment.