Describes cancer cells that have a change in the structure of the anaplastic lymphoma kinase (ALK) gene or a higher than normal amount of ALK protein on their surface. In normal cells, ALK helps control cell growth. When cancer cells have the changed ALK gene or make too much ALK protein, the cancer cells may grow more quickly. Knowing whether a cancer is ALK positive may help plan treatment. Cancers that may be ALK positive include neuroblastoma, non-small cell lung cancer, and anaplastic large cell lymphoma. Also called anaplastic lymphoma kinase-positive cancer.