Changing incidence of lobular carcinoma in situ of the breast.

Estimating the incidence of lobular carcinoma in situ (LCIS) of the breast is challenging because it lacks both clinical and mammographic signs and is usually an incidental finding in breast biopsies performed for other reasons. In general, population-based studies are believed to provide the most accurate measures, but few documenting changes in LCIS incidence rates over time have been reported. Age-adjusted age-specific LCIS incidence rates among women with no prior history of in situ or invasive breast carcinoma from 1978 to 1998 were obtained from nine population-based cancer registries that participate in the Surveillance, Epidemiology, and End Results (SEER) Program. Linear trends were evaluated using negative binomial regression. Overall, LCIS incidence rates increased fourfold (95% confidence interval, 2.9-5.6) over the study period. Specifically, they rose from 0.90/100,000 person-years in 1978-80 to 2.83/100,000 person-years in 1987-89, but then increased only modestly up to 1996-98 where the incidence rate was 3.19/100,000 person-years. However, among women 50-79 years of age, LCIS incidence rates increased continuously over the study's duration. In 1996-98, 50-59 year-olds had the highest incidence rate (11.47/100,000 person-years) and experienced the greatest absolute increase in incidence over the study period (9.48/100,000 person-years). LCIS incidence rates have steadily increased from 1978 to 1998 only among postmenopausal women. Further research is required to assess what factors are contributing to these trends.