Changing incidence rate of invasive lobular breast carcinoma among older women.

BACKGROUND

In 1998, an unusually large number of invasive lobular breast carcinoma cases were seen at the University of Washington. The purpose of this study was to assess whether the incidence rate of invasive lobular carcinoma has been increasing disproportionately compared with the incidence rate of invasive ductal carcinoma.

METHODS

Age specific and age-adjusted breast carcinoma incidence rates from 1977-1995 were obtained from the nine population-based cancer registries that participate in the Surveillance, Epidemiology, and End Results (SEER) program. Three histologic groupings were used: lobular, ductal, and all invasive breast carcinomas. Overall incidence rates for each grouping, as well as for each stage (local, regional, and distant), were obtained.

RESULTS

The rate of incidence of lobular carcinoma increased steadily from 1977-1995 in women age >/= 50 years whereas it remained stable in women age < 50 years. Alternatively, the rate of incidence of ductal carcinoma increased steadily from 1977-1987, but from 1987-1995 it remained relatively constant across all age groups.

CONCLUSIONS

The incidence rates of invasive lobular breast carcinomas increased steadily since 1977 whereas the incidence rates of invasive ductal carcinoma have plateaued since 1987. This rise occurred specifically among women age >/= 50 years and may be related to postmenopausal status. Further epidemiologic, clinical, and laboratory research is required to assess what factors are contributing to this trend.