Trends in incidence rates of invasive lobular and ductal breast carcinoma

Context Research has suggested that use of combined estrogen and progestin hormone replacement therapy (CHRT) increases breast cancer risk and that CHRT use more strongly associated with the risk of invasive lobular breast carcinoma than that invasive ductal carcinoma. Lobular carcinoma is less common than ductal carcinoma can be more difficult to diagnose because of its subtle elusive. infiltrative pattern. Objective To evaluate trends in invasive lobular and ductal carcinoma incidence from 1987 through 1999, during which time use of CHRT increased in the United Design Descriptive epidemiologic study. Setting Nine cancer registries that participate in the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute and that cover Atlanta, Ga; Detroit, Mich; San Francisco-Oakland, Calif; Seattle, Wash; and Connecticut, Hawaii, Iowa, New Mexico, and Utah., Population Women 30 years of age and older residing in the areas covered by the 9 SEER registries. Main Outcome Measures Proportional changes in incidence rates of invasive lobular and ductal carcinoma among women with no prior history of breast cancer. Results A total of 190458 women were included in this analysis who were identified through the registries as having invasive breast cancer; 7682 of the 198140 potentially eligible women (ie, those identified as not having in situ breast cancer) were I excluded from this analysis because stage of cancer was unknown. Invasive breast cancer incidence rates adjusted for age and for SEER historic stage increased 1.04-fold (95% confidence interval [CI], 1.004-1.07) from 1987-1999 (206.7/100000 to 214.1/100000, age-adjusted). However, incidence rates of tumors classified as lobular increased 1.52-fold (95% CI, 1.42-1.63), and those classified as mixed ductal-lobular increased 1.96-fold (95% CI, 1.80-2.14); rates of these types combined increased 1.65-fold (95% CI, 1.55-1.78) (19.8/100000 to 33.4/100000, age-adjusted). In contrast, ductal carcinoma rates remained largely constant (153.8/100000 to 155.3/100000, age-adjusted; proportional change, 1.03 [95% CI, 0.99-1.061). The proportion of breast cancers with a lobular component increased from 9.5% in 1987 to 15.6% in 1999. Conclusions Ductal carcinoma incidence rates remained essentially constant from 1987-1999 while lobular carcinoma rates increased steadily. This increase presents a clinical challenge given that lobular carcinoma is more difficult to detect than ductal carcinoma by both physical examination and mammography.