Time Trends in ILC and IDC Incidence Rates

From the 1970's to the mid-1980's, about 80% of all invasive breast carcinomas diagnosed in the USA had a ductal histology, and 5-10% had a lobular histology (2,3). However, ILC incidence rates have been increasing steadily among US women (21,22). The most recent of these studies documented a 65% increase in ILC incidence rates from 1987-1999, while incidence rates of IDC have remained essentially constant, increasing only 3% over this same time period (Figure 1) (22).

Figure 1. Incidence rates of all BC cases, IDC, and ILC in the USA, 1987-1999.

The proportion of all BC cases with a lobular histology increased from 9.6% in 1987 to 15.4% in 1999. ILC rates have also been increasing more rapidly than those for IDC in Geneva, Switzerland (23). In Geneva, ILC rates increased 14.4% per year from 1976-1999 while rates of IDC increased only 1.2% per year.

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