Swollen lymph nodes
Lymph nodes should be impossible to feel when you’re touching your breasts or the underarm area. In some cases, swollen lymph nodes in your breasts or your armpit would lead to an investigation of the root cause, and doctors would end up diagnosing breast cancer. However, in most cases, swollen lymph nodes are associated with infections and inflammation, probably due to a cut or bruise in a nearby area.
In any case, you need a physician to perform a full exam, and may even require lab tests to know the real cause of swollen lymph nodes. They are part of your immune system and would activate and start creating immune cells to defend your body from various pathogens, so you don’t need to think about breast cancer if that’s the only symptom you have.