Doctors have suspected that the hormone estrogen, which makes hormone-receptor-positive breast cancer grow, also may be associated with lung cancer. The large study reviewed here found that women treated with hormonal therapy for breast cancer were less likely to be diagnosed with lung cancer compared to women treated for breast cancer without hormonal therapy. These results were presented at the 2009 San Antonio Breast Cancer symposium.
The researchers looked at the medical records of 6,655 women from Switzerland who were diagnosed with breast cancer between 1980 and 2003. About 46% of the women were treated with hormonal therapy (called anti-estrogen therapy in the article). Tamoxifen was the hormonal therapy used most because the aromatase inhibitors weren't available when many of the women were diagnosed and treated. The women were followed through 2007.
Women who got hormonal therapy to treat breast cancer:
This article also mentions another large research study -- the Women's Health Initiative (WHI) -- that showed women who used combination hormone replacement therapy (HRT) that contained both estrogen and progesterone were 23% more likely to be diagnosed with and die from lung cancer compared to women who didn't use combination HRT.
These results suggest that estrogen plays a role in the development, growth, and spread of lung cancer. A better understanding of the link between estrogen and lung cancer could help doctors better pinpoint how estrogen fuels breast cancer and might lead to better cancer prevention strategies and new treatment strategies for breast, lung, and other cancers.
Stay tuned to Breastcancer.org for the latest news on research that offers the promise of better ways to prevent, diagnose, and treat breast cancer.
SAN ANTONIO (MedPage Today) -- Tamoxifen and other anti-estrogen therapies may reduce lung cancer mortality in women, according to observational study findings presented here.
Women who took endocrine therapy for breast cancer were 87% less likely to die from lung cancer than the general population (P<0.0001) despite similar lung cancer incidence, according to Elisabetta Rapiti, MD, MPH, of the University of Geneva, Switzerland, and colleagues.
But women with breast cancer who didn't take anti-estrogen therapy were no less likely to die from lung cancer than the general population (P=0.158), they reported at the San Antonio Breast Cancer Symposium.
These results lend further support to the "hypothesis that estrogen plays a role in lung cancer prognosis," Rapiti said at the conference.
Earlier this year, an analysis of the Women's Health Initiative in the The Lancet, suggested that women who had taken postmenopausal estrogen and progestin replacement therapy as part of the study were 23% more likely to die from lung cancer than women who had taken placebo.
While this overall difference was not significant (P=0.16), it started Rapiti's group thinking about the implications in the opposite direction.
"If combined hormone therapy is associated with an increased lung cancer mortality risk," she said at the session, "anti-estrogens may be associated with a decreased lung cancer mortality risk."
So they analyzed the population-based Geneva Cancer Registry to link breast cancer patients -- a population likely to have taken such drugs -- to lung cancer.
Of the 6,655 breast cancer patients included in the registry for 1980 through 2003, 46% had indeed received anti-estrogen therapy, which involved tamoxifen in most cases because the registry was weighted toward women treated in the pre-aromatase inhibitor era.
When followed through 2007 for lung cancer incidence, rates tended to be lower for anti-estrogen users, with a standardized incidence ratio of 0.63 compared with age- and time period-adjusted rates in the general population of the canton of Geneva (12 observed versus 19.1 expected cases, P=0.058).
For women who didn't get that therapy for breast cancer, the rate was no different than in the general population with a standardized incidence ratio of 1.12 (28 observed versus 25.0 expected cases, P=0.294).
Lung cancer deaths were significantly less common in women who took anti-estrogen therapy than in the general Geneva population -- two observed versus 15.3 expected -- for a standardized mortality ratio of 0.13 (95% CI 0.02 to 0.47).
But the group without endocrine therapy showed no such association, with 16 observed versus 21.1 expected cases (standardized mortality ratio 0.76, 95% CI 0.43 to 1.23).
Not surprisingly, many characteristics differed significantly between the women who took hormonal therapy and those who didn't, including more recent diagnoses.
A sensitivity analysis restricted to women diagnosed after 1990 showed results similar to those from the overall registry cohort.
Although tamoxifen and other hormonal therapy users were less likely to have missing information on smoking status, those who did have that information available showed no difference in smoking status by anti-estrogen use.
Rapiti cautioned that residual confounding was possible because of the study's observational design.
That means the investigators could not show causation, noted Jennifer Litton, MD, of the M.D. Anderson Cancer in Houston, who was not part of the study.
She also questioned whether the lung cancers found in the study were actually metastases to the lung, which might be expected to occur less often with better treatment.
The lung is one of the top sites to which breast cancer metastasizes, Litton noted.
Nevertheless, many types of cancer share common pathways, so what these findings mean for a shared mechanism is the part that is really interesting, she said.
She and Rapiti agreed that further prospective study is needed to confirm the association.
The researchers reported no conflicts of interest.
Litton reported no conflicts of interest.
Primary source: San Antonio Breast Cancer Symposium Source reference: Rapiti E, et al "Reduced Lung Cancer Mortality Risk among Breast Cancer Patients Treated with Anti-Estrogens" SABCS 2009; Abstract 35.
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