CD200 is considered as a marker of tumor progression since it is overexpressed on various cancers of both hematopoietic and non-hematopoietic origin, such as acute myeloid leukemia, multiple myeloma, hairy cell leukemias, B cell chronic leukemias, melanoma, and ovarian, rectal cancer, and bladder cancer, and its expression is associated with the worst prognosis (266–274). Here, CD200 is linked to cancer.