My kitty had a lump. It developed almost overnight on her right side near her back leg. It felt small, hard, and perfectly round like a little marble lodged under her skin. I wasn’t that worried about it. Mammary cancer in younger cats, especially those who were spayed before their first heat cycle is very rare. There’s a slightly higher risk factor in Siamese cats, but Morwen is your average, American shorthair with a bit of Bombay thrown in the mix, a sweet little kitty with a smooshed in nose and big yellow eyes. It certainly wasn’t mammary cancer, but maybe it was a lipoma, not unusual in cats, although not usually quick-growing or hard in nature. Lipomas, of which my elderly cocker spaniel had many, are usually squishy, round lumps filled with fat. Older dogs and cats often develop them and they are, usually, not dangerous. My cocker spaniel has had more than one aspirated and another two removed, all of which were benign.