<prompt> A middle-aged female present with lytic lesion in lower 13 of femur. Biopsy showed grooved nuclei and giant cells. No periosteal reaction seen. What is the confirmatory investigation for this case:-Serum PTHSerum CalcitoninCd1a and Langerin IHCMRI  <response>: Ans. C Cd1a and Langerin IHCRef: Apleys system of Orthopedics and Fracture 9th Ed; Page no-198 and 204The possible diagnosis in the given scenario is Langerhans cell histiocytosis LHC.Femur can be involved in LCH.LANGERHANS cells have a single large nucleus with characteristic folded or grooved nucleus Coffee-Bean appearance with small inconspicuous nucleoli.Visualization of the CD 1a surface marker is now considered sufficient to establish the diagnosis of LCH. 