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Women who lost weight had lower breast cancer risk

Even moderate weight loss in postmenopausal women might reduce risk of invasive breast cancer

Louise Prime

Tuesday, 09 October 2018

The incidence of invasive breast cancer among postmenopausal women who lost weight was lower than the risk among those who gained or maintained weight, according to new research. The authors of the study* published yesterday in Cancer, said although their study was observational, the results showed that women who lose weight might reduce their risk of breast cancer.

The research team, from the City of Hope National Medical Center in Duarte, California, pointed out that although it was already established that obesity is an established risk factor for postmenopausal breast cancer, studies into the relationship between weight loss and breast cancer risk have had inconsistent results. They evaluated associations between weight change and breast cancer risk in postmenopausal women in the Women’s Health Initiative Observational Study.

They studied 61,335 postmenopausal women with a normal mammogram and no history of breast cancer, whose body weight and height were measured – and body mass index (BMI) calculated – at baseline and again three years later. They categorised the women’s weight change over the three years as stable (<5% change), loss (≥5%), or gain (≥5%), and also asked the women whether or not any weight loss was intentional. Using multivariable Cox proportional hazard regression models, they then calculated associations between weight change and subsequent breast cancer incidence.

The researchers reported that during a mean follow-up of 11.4 years, there were 3,061 incident breast cancers. The 8,175 women who lost weight had a significantly lower risk of breast cancer compared with the 41,139 women whose weight remained stable (hazard ratio, HR 0.88); with no interaction by BMI. Their findings were not altered by adjustment for mammography (HR 0.88), and they found no significant difference by weight loss intentionality.

They also noted that weight gain (≥5%) (12,021 women) was not significantly associated with overall breast cancer risk (HR, 1.02), but it was significantly associated with a higher incidence of triple‐negative breast cancer incidence (HR, 1.54).

They said they had shown that even moderate, relatively short-term weight reduction was associated with a statistically significant reduction in breast cancer risk for postmenopausal women; and that although their results were observational, they tallied with randomised clinical trial evidence from the Women’s Health Initiative Dietary Modification trial – where adopting a low-fat dietary pattern that was associated with a similar magnitude of weight loss resulted in a significant improvement in breast cancer overall survival. They said: “These findings, taken together, provide strong correlative evidence that a modest weight loss programme can impact breast cancer."

They concluded: “Postmenopausal women who lose weight have lower breast cancer risk than those with stable weight. These findings suggest that postmenopausal women who lose weight may reduce their breast cancer risk.”

*Chlebowski RT, Luo J, Anderson GL, et al. Weight loss and breast cancer incidence in postmenopausal women. CANCER; Published Online: October 8, 2018 (DOI: 10.1002/cncr.31687). DOI:10.1002/cncr.31687

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