While generally infrequent, oncogenic deletions within MAP2K1 exons 2 and 3 are enriched in a small subset of human cancers including certain melanocytic lesions and particularly pediatric LCH (~30% of cases), and are mutually exclusive from the BRAF V600E variant [73,82–86]. Here, MAP2K1 is linked to Langerhans cell histiocytosis.