ALK and major depressive disorder: Several biological and pathologic characteristics have been shown to be associated with a higher risk of treatment failure in childhood ALK-positive ALCL over the past 15 years, i.e., high risk morphological pattern by the presence of a small cell (SC) or lymphohistiocytic (LH) pattern [12], positive PCR for NPM-ALK in peripheral blood (PB) and/or bone marrow (BM) at diagnosis (minimal disseminated disease; MDD) [13,14] and low anti-ALK antibody titers at diagnosis [15,16].