Women who use estrogen-only hormone replacement therapy don’t appear to be at increased risk of dying from lung cancer.

That’s according to a new analysis of earlier data from postmenopausal women who had had their uterus removed (hysterectomy).

Previous studies of women with intact uteruses had shown that taking combined estrogen and progestin - a synthetic version of the hormone progesterone - raised the chances of dying from lung cancer (see Reuters Health story of September 21, 2009).

Estrogen alone, however, resulted in only one more lung cancer death than placebo pills over nearly eight years, Dr. Rowan T. Chlebowski, of Harbor-UCLA Medical Center in Torrance, California, and colleagues reported Friday.

Overall, the researchers calculated that eight in 10,000 women would die from lung cancer every year, regardless of whether they took estrogen or placebo pills.

“These findings should be reassuring for women with previous hysterectomy, who use estrogen alone” for menopause symptoms, they write in the Journal of the National Cancer Institute.

Hormone replacement therapy (HRT) remains the most effective therapy for menopausal symptoms like severe hot flashes and night sweats and has been shown to preserve women’s bone mass.

But millions of women stopped using it after a large U.S. government study in 2002 found that postmenopausal women given estrogen-plus-progestin had higher risks of heart attack, stroke, breast cancer and blood clots than women given a placebo.

The new study was based on more than 10,000 women, aged 50 to 79 years, who were randomly assigned to take either an estrogen pill or placebo.

In the hormone group, 61 women (0.15 percent per year) developed lung cancer, compared to 54 (0.13 percent per year) in the placebo group. The researchers found this small difference could easily have been due to chance, but they add that it requires further investigation.

“This is good news, and one less thing to worry about for women who are taking estrogen alone,” said Dr. Nanette Santoro, who was not involved in the research, although she added that no single study can be definitive.

Santoro, chair of obstetrics and gynecology at the University of Colorado at Denver in Aurora, cautioned that estrogen alone was only an option for women who do not have a uterus.

For those who do, progesterone is necessary to prevent abnormal changes - and possibly cancer - in the lining of the uterus.

The new results agree with a large study published earlier this year that found no link between estrogen-only HRT and lung cancer risk (see Reuters Health story of February 24).

When compared with combined HRT, estrogen-only also seems to have a lower risk of breast cancer.

But it doesn’t protect against colon cancer, as combined HRT appears to do, and the risk of heart disease and stroke are comparable between the two treatments, Chlebowski and colleagues note.

Experts recommend that menopausal women weigh the benefits and risks of HRT with their doctor.

“Severity of symptoms, desire for relief, and prior adverse reactions to medications all go into the decision making process,” Santoro told Reuters Health by e-mail.

“Sometimes hormones are a great idea and sometimes they are not, so for most women I try to reassure them at first that we are very likely to be able to help reduce symptoms, but that some trial and error may be necessary.”

SOURCE:  the Journal of the National Cancer Institute, online August 13, 2010.