HMOX1 and neoplasm: Based on both HO-1 level directly measured in monocytes at days 15th and 33rd as well as relative HO-1 level changes in individual patients with different early treatment response (expressed as MRD level), we postulate that the altered HO-1 expression in bone marrow monocytes—but not in lymphocytes—may represent a response to stressful conditions, rather reflecting modulation of HO-1 in the tumor microenvironment as a potential mechanism of chemotherapy resistance.