National incidence rates for lobular and ductal breast cancers have not been available previously. Evidence suggests that the increased risk of breast cancer associated with combined hormone replacement therapy use is higher for invasive lobular cancers (ILC) than for invasive ductal cancers (IDC). This study provides U.S. incidence rates for these histologic types for both in situ and invasive cancers and assesses changes in the incidence of these cancers over time.
Data for this study included incident ductal and lobular breast cancer cases diagnosed from 1999 through 2004 in central cancer registries in 44 states and the District of Columbia from the National Program of Cancer Registries and the Surveillance, Epidemiology, and End Results program. We estimated incidence per 100,000 women by 10-year age groups, race, and ethnicity. We also assessed the percent change in invasive and in situ cancer incidence over time.
We observed distinct differences in the change of incidence over time between in situ and invasive lobular and ductal breast cancers. The age-adjusted rates of ILC and IDC declined an average of 4.6% and 3.3% per year, respectively. Overall, ILC decreased 20.5% from 1999 to 2004. The patterns of ductal and lobular in situ cancer incidence were not consistent over time, and the total change was negligible.
The declines in ILC observed in our study are consistent with a decrease in cancer incidence related to a reduced use of combined hormone replacement therapy. However, other factors could also be responsible for these changes.