Heterogeneity in risk factors for ductal and lobular breast carcinomas: A case-control study.

Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) of the breast are the most common histological subtypes of breast cancer. However, the associations and heterogeneity between histological subtypes and their risk factors are not well established. This study aimed to investigate risk factors for IDC and ILC. This case-control study included 1,009 incident breast cancer cases and 1,009 hospital controls, frequency-matched by age. Data were obtained from the patients' medical files and an interview administered via a questionnaire. Multinomial logistic regression was used and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. The heterogeneity of the associations was assessed using the Wald test. Family history of breast cancer was associated with IDC (OR 2.64, 95% CI: 1.97-3.55) but not ILC (OR 0.81, 95% CI: 0.42-1.57; p for heterogeneity <0.001). Conversely, a history of miscarriage was associated with ILC (OR 1.71, 95% CI: 1.17-2.51) but not IDC (OR 1.18, 95% CI: 0.95-1.46; p for heterogeneity = 0.04). Similarly, type 2 diabetes was associated with ILC but not IDC (p for heterogeneity = 0.02). Age at first delivery and breastfeeding were significantly associated with IDC but not ILC, though p values for heterogeneity did not reach the significance level. Deliberate weight loss and age at menarche were significantly associated with ILC but not IDC (p for heterogeneity ≥0.27). Smoking, history of benign breast disease and BMI were associated with both subtypes. The present study supports the hypothesis that IDC and ILC are etiologically distinct tumours.