The most common symptom is the appearance of a lump. This lump is usually hard and painless.
Breast cancer can also manifest itself in other ways:

• bulging in one area of the breast
  
• reduction in the volume of a breast
  
• retraction of the breast skin
  
• nipple inversion
  
• water-like liquid or blood coming out of the nipple
  
• redness or oedema (swelling) of the breast without apparent cause
  
• axillary lymph nodes (swelling in the armpit) usually on one side only, indurated and painless

These are some signs that can mean breast cancer or inflammatory diseases, such as mastitis, for example. But they are reasons to seek a doctor for a better evaluation.