Ans. (C) Cd1a and Langerin IHC(Ref: Apley's system of Orthopedics and Fracture 9th Ed; Page no-198 and 204)The 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.