Survival of patients with mixed phenotype acute leukemias: A large population-based study.

Little is known about the incidence and treatment outcome of patients with acute biphenotypic leukemias. The World Health Organization (WHO) established the term of acute leukemia of ambiguous phenotype in 2001 (revised in 2008) introducing the term of mixed phenotype acute leukemias. Using the database of the Surveillance, Epidemiology, and End Results registry (SEER), we identified 313 patients with mixed phenotype acute leukemias and compared them with 14,739 patients with acute lymphoblastic leukemia and 34,326 patients with acute myelogenous leukemias diagnosed between 2001 and 2011. As a further control group, 1777 patients were included who were not classified as myeloid, lymphoid or biphenotypic (other acute leukemias). The incidence of mixed phenotype acute leukemias is 0.35 cases/1,000,000 person-years. In a multivariate analysis, the prognosis depends strongly on age (as with other leukemias) and it has the worst outcome of all four types of leukemia. However, the prognosis has improved, comparing 2001-2005 with 2006-2011. We present the first comprehensive, population-based study of acute biphenotypic or mixed phenotype acute leukemias according to the WHO classification. Especially in older patients, the prognosis is unfavorable and new treatments should be investigated.