Unusual changes in the breast can be symptoms of breast cancer: Swelling; skin irritation or dimpling; breast pain; nipple pain or the nipple turning inward; redness, scaliness, or thickening of the nipple or breast skin; a nipple discharge other than breast milk; a lump in the underarm area (Source: The American Cancer Society)
In some cases, breast cancer may not cause any symptoms. The lump may be too small for you to feel or not cause any changes you notice on your own. Sometimes an abnormal area turns up on a screening mammogram, which can lead to further testing.
Sometimes the first sign of breast cancer is a lump or mass in the breast that you or your doctor can feel. A lump that is painless, hard, and has uneven edges is more likely to be cancer, although cancers can sometimes be tender, soft, and rounded. Have anything unusual checked by your doctor.
Some symptoms also can be signs of less serious conditions that are not cancerous such as an infection or a cyst. Again: It’s important to get any breast changes checked out promptly by a doctor.
Clinical breast exams are important. Starting in your 20s and 30s, women should have a clinical breast exam as part of a regular health exam by a health professional, preferably every 3 years. After age 40, women should have a breast exam by a health professional every year. (Source: The American Cancer Society)
Try to get in the habit of doing a breast self-examination once a month to familiarize yourself with how your breasts normally look and feel. Does something stand out as different from the rest (like a rock on a sandy beach)? Has anything changed? Talk to your doctor if any changes last over a full month's cycle or seem to get more obvious over time.
Examine yourself several days after your period ends when your breasts are least likely to be swollen and tender. If you are no longer having periods, choose a day that's easy to remember, such as the first or last day of the month.