Combined hormone-replacement therapy may boost incidence of rare form of breast cancer

May 31, 2000

The incidence of a rare form of breast cancer, called lobular carcinoma, is on the rise in postmenopausal women nationwide, and this increase may be associated with the widespread use of combined hormone-replacement therapy, according to researchers at the Fred Hutchinson Cancer Research Center in Seattle.

These findings are reported today in a pair of papers in the journal CANCER. The lead author of both papers is Christopher Li, M.D., a postdoctoral fellow in the Hutchinson Center's Public Health Sciences Division. Researchers from the University of Washington collaborated on one of the studies. Lobular breast cancer, which involves the lobules -- chambers in the breast that contain small milk-producing glands -- accounts for only 5 percent to 10 percent of all invasive breast cancer cases. The most common form of breast cancer, representing up to 85 percent of cases, is ductal carcinoma, which involves the complex network of milk ducts that distribute milk from the lobules through the breast and into the nipple.

While much rarer than ductal breast cancer, lobular carcinoma appears to be on the rise in postmenopausal women, particularly among those who take combination hormone therapy (progestin and estrogen).

In one paper, Li and colleagues at the Hutchinson Center report a 2.6-fold increase in the incidence of lobular breast cancer among postmenopausal women who took combined hormone-replacement therapy for six months or more, as compared to those who took no hormones. This study involved nearly 1,000 Seattle-area women (half with breast cancer, half without).

In the other paper, Li and colleagues at the Hutchinson Center and UW report a significant increase in lobular breast cancer among postmenopausal women nationwide. For this study, the researchers looked at data from the Surveillance, Epidemiology and End Results program, or SEER, a national cancer registry operated by the National Cancer Institute. In analyzing data from 1977 to 1995, the researchers found a greater than 70 percent increase in lobular cancer in women registered at six of nine SEER data-collection sites. In comparison, the increase in ductal carcinoma was less than 40 percent among cases registered at six of the nine SEER sites. This study population included more than 120 million women nationwide.

"Although preliminary, our studies suggest that the incidence of lobular breast cancer is increasing nationwide and that the use of postmenopausal hormone-replacement therapy, specifically the use of combined estrogen plus progestin preparations, may be contributing to this increase," Li says. "However, future studies are required to confirm these findings, and it is important to note that lobular tumors represent only 5 percent to 10 percent of all breast carcinomas."
Both studies were funded by the National Cancer Institute.

Editor's note: For a copy of either paper or to arrange an interview with lead author Christopher Li, M.D., please contact Kristen Woodward, 206-667-5095.

The Fred Hutchinson Cancer Research Center is an independent, nonprofit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone-marrow transplantation, the Center's four scientific divisions collaborate to form a unique environment for conducting basic and applied science. The Hutchinson Center is the only National Cancer Institute-designated comprehensive cancer center in the Pacific Northwest. For more information, visit the Center's Web site at

Advancing knowledge, saving lives

Fred Hutchinson Cancer Research Center

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