Can I remove PMI early if my home value increased significantly?

I bought my home 2 years ago with 10% down and have been paying PMI. My neighborhood has seen a lot of appreciation — Zillow shows my home is now worth about 25% more than when I bought it. Based on the new value, my LTV would be well under 80%. Can I request PMI removal based on the current market value, or does it have to be based on the original purchase price?