A 2 year old child presents with scattered lesions in the skull. Biopsy revealed Langerhans giant cells. The most commonly associated is marker with this condition will be -

Ans. is 'a' i.e., CD1a o The presence of Birbeck granules in the cytoplasm of tumor cells is characteristic of Langerhans cell histiocytosis. o As Birbeck granules are not seen in all tumor cells by election microscopy the detection of S-100 and CD1a expression by immunohistochemical techniques aids in the diagnosis. o Other immunohistochemical markers of Langerhans cell histiocytosis are HLA-DR, Langerin (CD 207), and CD 68.