C

Reasoning: Giant-cell tumor of bone typically affects young adults aged 20–40 yr [Moser, 1990, PMID 2296699] and is considered histologically benign yet can rarely metastasize to the lungs [Kitano, 1999, PMID 10658380]. Histologically, the matrix is composed of proliferating mononuclear stromal cells; the multinucleated osteoclast-like giant cells are reactive and do not constitute the neoplastic (proliferative) component [Wülling, 2001, PMID 11501745]. Therefore, statement C is incorrect.