The findings were also presented at the American Association for Cancer Research Conference. Myeloproliferative neoplasms, or MPNs, are rare blood cancers that begin in the bone marrow, where blood cells are made. In these diseases, the body produces too many blood cells. As a result, some people may receive treatment even though their condition may not be a true blood cancer. Surprisingly, many of their blood cells showed patterns more consistent with normal aging than cancer.