The study included 5,204 women with invasive breast cancer who were between the ages 30 to 55 when enrolled in the study in 1976. The researchers found that women who weighed more before they were diagnosed with breast cancer and those who were lean but gained weight after diagnosis and treatment tended to have worse survival outcomes. Intriguingly, the association was strongest in women who did not smoke.
“By combining smokers and non-smokers in analyses, it may be more difficult to understand the true relationship between weight and survival. This study suggests a more complex relationship between weight and breast cancer survival than was originally considered,” said lead researcher Candyce Kroenke, Sc.D., M.P.H., and an instructor at Harvard Medical School.
Among non-smokers, the study showed that overweight women were 1.5 times as likely and obese women two times as likely to die during follow-up than were women with normal BMIs before diagnosis. It also showed that women with substantial weight gain after diagnosis had a more than 50 percent greater risk of death or recurrence than women who maintained their weight after diagnosis. Finally, the strongest link between weight gain and death/recurrence were in pre-menopausal women, those with early stage cancer and those who were lean prior to diagnosis.