Thickening near your armpit. If the skin on the upper corner of your chest (where it intersects with your armpit) feels thick or knotty, it could indicate a tumor that has spread to the nearby lymph nodes.
Scaling around the areola. If any section of the areola seems scaly or you notice a sore there that doesn’t heal after a few weeks, you may have a rare form of breast cancer called Paget’s disease.
A puckered texture. As a tumor grows in breast tissue, it can crowd out ligaments that make skin firm and smooth, causing a dimpled, creased appearance.
Changes in color. A reddish skin inflammation that appears on any part of your pair and persists for more than a few weeks may be a sign of the disease.
An inverted nipple. While some women are born with one or both their nipples turned inward, one that suddenly retracts is a sign that a lump may be growing under the breast’s areola.
Source: Eva Singletary, MD, professor of Surgicaloncology at the University of Texas MD Anderson Cancer Center, Houston