Dianatinasab M, et al. - In this case-control study, researchers investigated risk factors for invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) of the breast, to determine the associations and heterogeneity between these histological subtypes and their risk factors. Participants were 1,009 incident breast cancer cases and 1009 hospital controls, frequency-matched by age. By means of medical files and a questionnaire, participants were assessed. They used the Wald test to evaluate the heterogeneity. The factors that showed associations with IDC but not ILC included a family history of breast cancer, age at first delivery and breastfeeding (though P values for heterogeneity did not reach the significance level). The factors that were found to have associations with ILC but not IDC included a history of miscarriage, type 2 diabetes, deliberate weight loss and age at menarche (significantly associated). Smoking, history of benign breast disease and BMI were related to both subtypes. An etiological distinction between IDC and ILC was supported.