Rare breast cancer on the rise

Li study indicates increase in hard-to-diagnose lobular tumors may be linked with higher use of hormone therapy

A new nationwide study indicates a significant, steady increase in the incidence of a relatively rare and hard-to-diagnose form of breast cancer thought to be associated with the use of hormone-replacement therapy.

Led by Dr. Christopher Li of the Public Health Sciences Division, the study found that rates of lobular breast cancer jumped 65 percent over a 13-year period. The incidence of the most common type, known as ductal breast cancer, remained largely constant.

Increased risk of lobular cancer has been linked to use of combined estrogen and progestin hormone therapy in menopausal women. Researchers suspect that the rising incidence of such cancer in the United States may reflect the increased use of the therapy during the last 25 years.

"Our study, which extends our previous analysis through 1999, adds to the evidence that combined-hormone therapy is associated with the increase in lobular cancer," Li said.

In addition to evaluating breast-cancer trends over a longer time period, the new study also reported that the rate of mixed ductal-lobular carcinoma, another rare form of breast cancer, doubled during the time period studied.

The results appear in the March 19 edition of the Journal of the American Medical Association. Co-authors included Dr. Ben Anderson, a University of Washington breast surgeon and clinical medical director of the UW Breast Care and Cancer Research Program; Dr. Janet Daling, Public Health Sciences Division; and Dr. Roger Moe, also a UW breast surgeon.

Li and colleagues used data from nine cancer registries around the nation to identify 190,458 women diagnosed with invasive breast cancer between 1987 through 1999. Of these cases, nearly 73 percent were invasive ductal carcinoma, 7.6 percent were invasive lobular carcinoma and about 5 percent were invasive mixed ductal-lobular carcinoma.

During the 13-year period, the overall incidence of invasive breast cancer increased by 4 percent. The incidence of all lobular cancers increased by 65 percent. Straight lobular cancers jumped by 50 percent, while those of the mixed ductal-lobular form nearly doubled. Ductal carcinoma rates remained constant.

The researchers did not analyze whether women were users of hormone-replacement therapy. Lobular cancer involves the lobules, the chambers in the breast that contain small milk-producing glands. Progestin, one of the components of combined hormone-replacement therapy, is known to stimulate growth of the lobules. Ductal carcinoma involves the complex network of milk ducts that distribute milk from the lobules through the breast and into the nipple.