Breastfeeding and risk of breast cancer: a metaanalysis of published studies.

Evidence in favour of an association of breastfeeding with a breast cancer risk reduction remains limited and inconsistent. To evaluate the relation between breastfeeding and breast cancer, a meta-analysis based on a review of the literature was carried out, using as variables ever/never breastfeeding and duration of breastfeeding. Menopausal status at the time of diagnosis of breast cancer was considered to be a potential effect modifier. Only case-control studies could be included in the final analysis. A slight but significant decreased risk of breast cancer was observed in ever breastfeeding, compared with never breastfeeding parous women, using both the fixed and random-effect models. This decrease was more pronounced in non-menopausal women at the time of diagnosis of breast cancer and in long-term breastfeeding women. Hence, breastfeeding appeared to be a protective factor but was of small magnitude compared with other known risk factors for breast cancer. Whether this result should imply a modification in the attitude of both health care providers and women towards breastfeeding, which represents one of the few identified protective factors which is under the control of the mother, and is thus (theoretically) modifiable, remains questionable.