Eight years is a long time. It's possible this book isn't still in print. Google it to see who published it and see if you can find out how it's selling. They suggest using comps published within the past five years, so it would be old as a comp. You need a second comp that's newer to make it work. If it is in print, I wouldn't sub to this agent, if there is one, or publisher. If this book isn't popular, it may not be a good comp. But if it's too popular, it's not good comp either.
Now, think about the actual story. Do the same events happen or is it just the same type of story. There are plenty of stories about an ugly duckling or other misfit that doesn't seem to fit in until everyone sees something special about them. Other themes are pretty common too. As long as you have a unique spin on the tried and true, that's fine. But if you have the same actions, you may not be able to market this book both because of copyright and because the tried and true need freshening to sell. See if you can make your spin more unique.
Everything depends on how close this really is to your work. It's sales are less of a consideration though they can indicate the market for similar books. I hope this makes sense.