ALK and anaplastic large cell lymphoma: Four distinct entities of ALCL, including ALK+ ALCL, ALK− ALCL (represent 15–25% of non-cutaneous PTCLs in total), primary cutaneous ALCL (PC-ALCL), and breast prosthesis implantation ALCL (BI-ALCL), share common pathological features: a large-cell anaplastic morphology, strong CD30 expression and frequent phospho-STAT3 activation.