Hormone use for just 3 years ups lobular breast cancer risk

January 15, 2008

NEW YORK (Reuters Health) - New research indicates that as little as 3 years of using combined estrogen and progestin menopausal hormone therapy (CHT) substantially increases the risk of developing lobular breast carcinoma.

"Previous studies suggest that only women who use these hormones for at least 5 years have an increase in breast cancer risk, but none have evaluated how shorter durations of use impact risk of lobular breast cancer," lead author Dr. Christopher I. Li told Reuters Health.

Dr. Li, from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues note that invasive ductal carcinoma is still the most common type of breast cancer in the US (about 70% of cases), but invasive lobular and mixed ductal-lobular carcinomas now make up about 16% of cases.

As reported in the January issue of Cancer Epidemiology, Biomarkers, and Prevention, the researchers conducted a population-based case-control study that included 324 lobular, 524 ductal, and 196 ductal-lobular breast cancer cases diagnosed between 2000 and 2004. The controls consisted of 469 women randomly picked from the general population.

Current CHT use increased the risks of lobular and ductal-lobular carcinomas, by 2.7- and 3.3-fold, respectively. At least 3 years of CHT use was needed to see an increased risk. Further analysis showed that, for ductal-lobular carcinomas, CHT use increased the risk only for those dominated by the lobular histology.

Current CHT use was associated with a 1.4-fold increased risk of ductal carcinoma, but this did not reach statistical significance.

"Overall, I do not think that these findings substantially change current recommendations regarding use of hormone therapy. Women considering hormone use should still try and use hormones for the shortest time possible and should use the lowest dose possible," Dr. Li said.

As for further research, he commented, "The underlying biology explaining why hormones may impact the risk of certain types of breast cancer more strongly than other types remains poorly understood, so this is a problem we are actively studying. Also, now that various risks associated with hormone use have been identified, many women have started using other types of hormones, such as natural hormones, but very little is known about how these different types of hormones are related to breast cancer risk."