Patients with systemic ALCL are divided into two groups, depending on whether or not their cells have an abnormal form of a protein on their surface called "anaplastic lymphoma kinase" (ALK). Although both lymphomas are treated as aggressive (fast-growing) lymphomas, the disease course is different in patients who have ALK-positive (have the abnormal protein) or ALK-negative (do not have the abnormal protein) ALCL.