This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
True about parosteal osteosarcoma - 
Select and explain. 
A. Same prognosis as medullary type, B. Never go to medulla, C. May involve medulla, D. All of the above
C: May involve medulla
Answer: C: May involve medulla 
Explanation: This question is quite different from previous one.
Though medullary cavity is not involved in parosteal osteosarcoma, some dedifferentiated type (grao sarcoma may involve medullary cavity. -- DD of bone tumor.