Q: Given a passage with a question and an answer to that question, classify if the answer actually answers the question into 'yes' or 'no'. Output 'yes' if the answer answers the question and output 'no' if the answer does not answer the question.
Question: Are differences in dural penetration of clival chordomas associated with different prognosis and expression of platelet-derived growth factor receptor-?
Answer: Clival chordomas have different degrees of dural penetration. Patients with chordomas with serious dural penetration have poorer prognosis. Higher expression of PDGFR- is related to more serious dural penetration of clival chordomas.
A:
yes