My mother had stage IV breast cancer. She waited way too long, almost too long to go in. She felt a lump around Christmas and didn't go in to have it checked out until late August. By that time it was painful, outward growing and awful looking. If I had a picture, I'd post it. My point is that had she gone in for regular mamograms (she was 66 and had never had one) or gone in at the first sign of that lump she always said it wouldn't have hurt so bad. By the time she went in, it was painful and it had spread. At the beginnng, she said it didn't hurt at all. She found it when she was rubbing some lotion on one morning. She just kept putting it off and then was too embarrassed to go in and say "look at this" and have them ask her why the hell she hadn't come in earlier. I have to say when she did go in, not one doctor ever scolded her or made her feel bad about waiting so long.
As soon as it started shrinking with chemo it hurt less. Again, I want to stress her example is extreme. This thing was literally so big it couldn't grow inside anymore. They then removed it with a lumpetectomy after she had some chemo, then gave her more chemo. After all that, her breast wasn't tender at all.
If you have a lump, please have it checked out. I don't think pain or lack thereof is a determination of whether or not its cancer.