Context Research has suggested that use of combined estrogen and progestin hormone
replacement therapy (CHRT) increases breast cancer risk and that CHRT use
is more strongly associated with the risk of invasive lobular breast carcinoma
than that of invasive ductal carcinoma. Lobular carcinoma is less common than
ductal carcinoma but can be more difficult to diagnose because of its subtle
elusive infiltrative pattern.
Objective To evaluate trends in invasive lobular and ductal carcinoma incidence
rates from 1987 through 1999, during which time use of CHRT increased in the
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 190 458 women were included in this analysis who were
identified through the registries as having invasive breast cancer; 7682 of
the 198 140 potentially eligible women (ie, those identified as not having
in situ breast cancer) were 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 (206.7/100 000 to 214.1/100 000, 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) (19.8/100 000 to 33.4/100 000, age-adjusted). In
contrast, ductal carcinoma rates remained largely constant (153.8/100 000
to 155.3/100 000, age-adjusted; proportional change, 1.03 [95% CI, 0.99-1.06]).
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.