Could be, but now that you say that, I just thought about how it went with my mother's breast cancer surgery. They removed lymph nodes and THEN tested them. I believe if it was 3 or more testing positive, they considered it to be spread, and then she had 4. (It was one over, whatever the baseline was) - but she lived 13 more years, and didn't die of cancer.
So, that is probably it - removing them to test them.
Or, to prevent spreading as you said.