ALK and neoplasm: In NB, intratumor heterogeneity has been reported for MNA and segmental chromosome alterations.47-49 The coexistence of ALK nonmutated and mutated cells within a single tumor suggests that these different subclones might coexist in an advantageous equilibrium, which might crucially affect the dynamics of cancer progression.50,51 Correlation with pathologic findings, single-cell RNA or DNA experiments, and in situ approaches will elucidate how ALK-mutated cells are distributed throughout an NB.