Background. Obesity and body-fat distribution have been associated wit
h the incidence of breast and endometrial cancers. It may be critical
to determine if the timing of weight gain during periods of hormonal c
hange, such as menarche, pregnancy, or menopause, has different biolog
ic effects, especially secondary to differences in the localization of
body fat during these periods. The objective of the current study was
to determine if excess weight in any particular decade of life or the
timing of weight gain was more significant relative to breast cancer
risk. Methods. Anthropometric, medical, and hormonal histories were ob
tained from 218 consecutively recruited, newly diagnosed patients with
breast cancer admitted to the H. Lee Moffitt Cancer Center and Resear
ch Institute (Tampa, FL) and 436 control subjects, matched in a two to
one ratio for age and menopausal status. Results. A weight gain of 15
pounds or more was observed for 63.8% of the patients compared with 4
9.3% control subjects (P = 0.0006) from age 30 to current age. Similar
ly, more than 48% of cases gained more than 15 pounds from ages 16 to
30 compared with 37% (P = 0.01) of the control population. Although we
ight gain from age 16 to adulthood was significantly higher in patient
s with breast cancer at each decade when compared with control subject
s, a significant and independent association between weight at age 30
(P < 0.0001) and risk of breast cancer was noted. Conclusion. Women wh
o progressively gain weight from puberty to adulthood, and specificall
y in the third decade of life, should be considered at a higher risk f
or developing breast cancer.