Those whose breasts suddenly become tender after starting estrogen plus progestin HRT are far more likely to have breast cancer, a new study has discovered.

Researchers at University of California at Los Angeles (UCLA) are not sure what the relationship is between breast tenderness and cancer, but think it may be because HRT causes breast tissue cells to multiply more rapidly.

The UCLA researchers made the discovery after analysing the health profile of 8,506 women taking HRT and comparing them with 8,102 women who are not taking the drug.

(Source: Archives of Internal Medicine, 2009; 169: 1684-91).