One breast larger than the other. breast-feeding for 3 mos. how can you tell if it's due to cancer? seems to be larger than normal, comparing sides.

Unlikely: Breasts are usually not the same size. You did not say whether the larger breast is red or painful, or if you have had problem with enough milk on that side. Breast cancer is unlikely but not impossible at age 31. Other causes of breast enlargement more likely (infection, obstructed milk duct). See your doctor for an exam.

Breast asymetry: Very few women have 2 breasts of the same exact size. Most of the time one is slightly larger. During breast feeding the human breast can change dramatically in size. If one was slightly larger to start off with, it's likely they may be even a greater difference in size as they grow during lactation. A larger breast due to caner is possible but extremely unlikely. Usually present as a mass.

Highly unlikely: to be cancer in this setting.Breast size asymmetry is not uncommon. Still, if you notice a difference in your breast self exam, you should see your doctor for an evaluation.