evidence: For information on other known and possible breast cancer risk factors, see: [...] A woman with cancer in one breast has a higher risk of developing a new cancer in the other breast or in another part of the same breast. (This is different from a recurrence or return of the first cancer.) Although this risk is low overall, it's even higher for younger women with breast cancer. [...] Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Breasts appear denser on a mammogram when they have more glandular and fibrous tissue and less fatty tissue. Women with dense breasts on mammogram have a higher risk of breast cancer than women with average breast density. Unfortunately, dense breast tissue can also make it harder to see cancers on mammograms.