CD1A and Langerhans cell histiocytosis: To date, only 3 cases of CD1a-negative LCH have been reported, highlighting the rarity of this variant: a 9-year-old boy with central nervous system involvement showing S100 positivity but CD1a negativity [18], a 35-year-old woman with skull lesions positive for S100 but negative for CD1a [19], and a 13-year-old girl with a frontal bone lesion negative for CD1a and S100 [20].