An excisional biopsy is done when cancer is suspected. However, it doesn't mean cancer is confirmed. It's a test for cancer, and you don't have a cancer diagnosis until the results come back.
A benefit of excisional biopsies is that no matter your diagnosis, your tumor will already be removed. In some cases, your excisional biopsy might be all the treatment you need. Plus, even if it turns out your tumor is noncancerous, you won't have to worry about future tests or decisions.