Genetic complexity among systemic mastocytosis subtypes. Clinical characteristics, morphology, and genetics should be seen as complementary tools for subtyping of SM. The presence of multilineage KIT and/or a multimutated molecular profile may contribute to a more advanced presentation of SM and/or disease evolution. For example, multilineage ISM is prone to progression to advanced SM, and prognosis may be equal or even worse than in MCL without multilineage involvement, additional somatic mutations, or C findings.