Factors affecting rise in the incidence of infiltrating lobular carcinoma of the breast

Background: Infiltrating ductal carcinoma and infiltrating lobular carcinoma account for more than 90% of all invasive breast cancer histological types. The rate of ILC is reported to be increasing steadily in the United States and Europe. Objectives: To describe the trend in the incidence of ILC in a large cohort of patients who underwent surgery in a single institution over an 18 year period. Methods: Our comprehensive database of 2175 consecutive patients with invasive breast cancer diagnosed during the period 1992-2009 served for the analysis. Several potential factors associated with lobular carcinoma as compared with ductal carcinoma were evaluated. Results: During this period, a 2.4-fold increase in the incidence of pure ILC was noted, from 4.6% in the years 1992-1994 to 10.9% in 2004-2006, followed by a modest decrease to 8.7% in 2007-2009. A significant association of lobular malignancies with external hormonal use was noted, including hormone replacement therapy exposure in patients diagnosed at age 50-64, and ovarian overstimulation during in vitro fertilization in those diagnosed at age 50 or less. Conclusions: Better diagnostic tools - such as the liberal use of ultrasound and magnetic resonance imaging - and more accurate pathological definition for ILC type appear to influence the changes in the incidence of ILC in the subgroups of invasive breast cancer.