The effects of immunotherapy are numerous and are still being discovered. We present a case report of a patient who received dasatinib for chronic myeloid leukemia. A colonoscopy was performed due to a positive fecal occult blood test and colitis was observed. Furthermore, she also had a cytomegalovirus infection. This case highlights the importance to detect cases of immunomodulatory drugs induced colitis by the fecal occult blood test.