Can a surgeon tell right away?

Can a surgeon tell right away if a lymph node is cancer? Or, does it have to be found under microscope? My son had a lymph node removed friday from his neck. He was put to sleep. The surgeon said he was 99% sure it was ok, that he did not see anything. He sent it to get biopsied. Just wandering if you can tell by looking at one? Hope this made sense!