Several studies have found associations between breastfeeding and reduced risk of pre-menopausal breast cancer. However the results are inconsistent, and data from large prospective cohort studies are lacking. Such a large study was carried out in the USA (1) using data from 60,075 parous women participating in a prospective cohort study. Women who had ever breastfed were less likely to suffer premenopausal breast cancer compared with women who had never breastfed and this association was modified by family history of breast cancer. The authors conclude that a history of having breastfed was inversely associated with incidence of breast cancer among women with a family history of breast cancer.

Several studies have found associations between breastfeeding and reduced ovarian cancer rates, however inconsistencies have been noted, particularly related to breastfeeding duration and to the type of ovarian cancer. An Australia-wide population-based case-control study (2) of epithelial ovarian cancer between 2001 and 2005 (1,092 cases and 1,288 controls) looked at parous women and their responses to a reproductive/lifestyle questionnaire. The researchers found a strong association between total duration of breastfeeding (all episodes) and reduced ovarian cancer occurrence, with protection increasing per month of breastfeeding. They conclude that a long total duration of breastfeeding appears to be associated with a substantial reduction in the overall risk of ovarian cancer but that this may vary according to histological subtype.