"A new painless, firm breast lump with irregular margins is a potential symptom of breast cancer," says Dr. Sandhya Pruthi, a breast cancer researcher at the Mayo Clinic. "The cancer diagnosis is confirmed following a biopsy of the lump." She notes that usually, women who are newly diagnosed with breast cancer are healthy and don't feel sick at all.
Another potential symptom/sign of breast cancer, Pruthi notes, is a new onset of persistent redness on the skin overtop the breast with an orange peel appearance. This would also need a biopsy to confirm a diagnosis of breast cancer.