Can kneading be a sign of pain or unhappiness?

As I mentioned a few weeks ago, I have a cat with a tumor. She has
gone downhill quite a bit. I'm now having to decide what to do. One of
the things that is throwing me off is how she sometimes briefly kneads
me. It might only be just once or twice that she does it, usually when
she sits on my lap. I don't know what to make of that. Could she be in
pain or discomfort and still knead me as a sign of affection? I just
don't know what it means. I don't know if she wants me to continue
letting her fight this tumor or if she's ready to go. If I knew what
kneading means exactly, it would help my decision. Just like with
purring, the fact that she's purring doesn't necessarily mean she's
happy, she could be in pain. Does kneading work the same way?