Researchers at Fred Hutchinson Cancer Research Center have revealed that combined estrogen/progestin hormone-replacement therapy (HRT) taken by postmenopausal for around three years or more leads to a fourfold increased risk of developing various forms of lobular breast cancer.
The study led by Christopher I. Li, M.D., Ph.D., an associate member of the Hutchinson Center's Public Health Sciences Division, has confirmed earlier reports linking between combined hormone-therapy use and increased risk of lobular breast cancers.
It is the first of its kind study examining the recency and duration of hormone use and the first to include a centralized pathological review of tumor specimens to confirm their histological type: ductal, lobular or mixed ductal-lobular.
"Previous research indicated that five or more years of combined hormone-therapy use was necessary to increase overall breast-cancer risk. Our study, the first specifically designed to evaluate the relationship between combined HRT and lobular breast cancers, suggests that a significantly shorter length of exposure to such hormones may confer an increased risk," said Li.
Lobular cancer is concerned with lobules, or chambers, in the breast that contains milk-producing glands and is hormonally sensitive and therefore more treatable than the more common ductal variety, arising in the ducts carrying milk from the lobules to the nipple.
Also, lobular breast tumors pose a clinical challenge as they are more difficult to detect both by clinical examination and by mammography than ductal cancers.
For the study, researchers examined hormone-replacement status in more than 1,500 postmenopausal women in western Washington. This included 1,044 breast-cancer cases (324 lobular, 196 mixed ductal-lobular and 524 ductal) and 469 controls. Tumor status was also confirmed through centralized examination of breast tissue.
According to the results, a 2.7-fold and 3.3-fold elevated risk of lobular and ductal-lobular cancer, respectively, was detected in current users of combined HRT, irrespective of tumor stage, size or number of lymph nodes involved.
Only women who used combined HRT for three or more years faced an increased risk of lobular cancer. In case of mixed ductal-lobular cases, hormone therapy increased the risk of tumors that were predominantly lobular but not tumors that had predominantly ductal characteristics.
"Our research suggests that the use of postmenopausal hormone-replacement therapy, specifically the use of combined estrogen-plus-progestin preparations, may be contributing to this increase," said Li.
He added: "These findings are still of considerable public-health importance considering the estimated 57 million prescriptions for menopausal hormone therapy that continue to be filled in the United States.
The study was published in the recent issue of Cancer Epidemiology, Biomarkers and Prevention