IDO1 and acute myeloid leukemia: Subsequent studies showed that serum KYN levels alone [133] or in combination with expression levels of IDO1 [134] can have an important prognostic role in AML and also in other hematological malignancies such as adult T-cell leukemia/lymphoma [135,136], peripheral T-cell lymphoma [137] and in diffuse large B-cell lymphoma [138].