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Lung cancer risk equal for all nonsmokers

Scripps Howard News Service
May 17, 2006 - Women who've never smoked are not more likely to die from lung cancer than their male counterparts, according to a new study from the American Cancer Society that counters recent conventional wisdom about the disease.

While it is true that about 20 percent of female and 10 percent of male lung-cancer patients never smoked, compared to about 1 in 10 male lung-cancer patients, "the reason appears to be unrelated to cancer risk," said Dr. Michael Thun, chief epidemiologist for the Cancer Society and lead author of the new study, published Wednesday in the Journal of the National Cancer Institute.

"Instead, it appears to be the result of the fact that there are far more women than men over the age of 60 who never smoked. Census data show there are about 16.2 million women compared to just 6.4 million men in the U.S. who are over 60 and never smoked."

The average age of an American getting a lung-cancer diagnosis is 70.

Smoking at some point in a lifetime accounts for 85 percent to 90 percent of lung-cancer cases. , but the Cancer Society estimates that 15,000 Americans who never smoked die from lung cancer each year. However, Thun says the number of nonsmokers diagnosed with the disease doesn't seem to be rising significantly.

Experts sayOverall, lung-cancer deaths have increased by 20 percent for men since 1988, compared to a 150 percent increase among women because . But experts say this is mainly due to the fact that smoking rates have declined more slowly among women at a much slower pace than among men since the 1960s.

Many women believe that smoking helps them control their weight, and once they start smoking, women often find it harder to quit than men do. Considerable research suggests that women may actually be more susceptible to the carcinogenic chemicals from tobacco smoke than are men.

The new study looked at smoking status and age, sex and race-specific lung-cancer death rates among more than 940,000 Americans enrolled in one of two national cancer-prevention studies, one from 1960 through 1972, the second that began in 1982 and is ongoing, with the latest mortality data entered from 2002.

The study group included 1,498 people who never smoked, but died from lung cancer.

Thun and colleagues found that the annual rate of dying from lung cancer per 100,000 people was 18.7 for men compared with 12.3 in women during the earlier study period, and 17.1 in men versus 14.7 in women who never smoked in the more recent study period.

The researcher said the narrowing of the gap between men and women likely reflected a decrease in the death rate of men ages 35 to 69 between the two studies and an increase in the death rate among women ages 70 to 84 over the same time period.

This probably reflects more complete diagnosis due to greater awareness of lung cancer in women and the availability of newer diagnostic tools that can detect cancer in the periphery of the lung without major chest surgery.

"Our findings are reassuring for women who've never smoked and who may have been alarmed by recent reports indicating that their risk was higher than it actually is," said Thun.

Because they may be more sensitive to tobacco smoke, it's thought that women are at greater cancer risk from passive smoking, but lung cancer can also be caused by exposure to asbestos, radon and other cancer-causing material in workplace, home and medical settings.

Other research suggests that higher estrogen levels and greater prevalence than men of one or more genetic mutations may increase the cancer risk for women nonsmokers.

Lung cancer is the leading cancer killer for men and women, claiming the lives of some 90,000 men and 73,000 women annually in the United States.

On the Net: http://www.cancer.org
(Contact Lee Bowman at BowmanL(at)SHNS.com. Distributed by Scripps Howard News Service, http://www.shns.com)

Bexarotene is a potential lung cancer preventative with few side effects

Researchers at Washington University School of Medicine in St. Louis reported that a compound related to vitamin A shows promise in preventing or slowing tumor growth in mice prone to lung cancer. The compound, called Bexarotene, doesn't cause the severe skin irritations that have limited the use of other vitamin A derivatives in cancer therapies.

" In the cancer prevention field, you look for drugs that can be given to healthy patients who have a higher risk of developing cancer," says Ming You, of the Chemoprevention Program at the Siteman Cancer Center. " These patients wouldn't want to take a medication that makes them feel sick when they don't have cancer. So the drugs should be very well-tolerated and not cause harmful side effects."

In other studies, Bexarotene showed some promise in cancer treatment. It extended survival in patients with non-small cell lung cancer, the most common type of lung cancer and one that has a five-year survival rate of less than 5 percent when diagnosed at the advanced stage.

In the current study, published in the Oncogene, Yian Wang, and colleagues demonstrate that lung-cancer-susceptible mice receiving non-toxic doses of Bexarotene ended up with fewer and smaller benign and malignant tumors than mice that were not treated with Bexarotene.

The researchers saw a reduction of almost 50 percent in terms of total tumor burden in mice who were given Bexarotene for 12 weeks after the animals had already developed benign tumors following injection of a lung carcinogen. Bexarotene also inhibited the progression of benign to malignant tumors by about 50 percent. The mice were engineered to have the genetic alterations seen in human lung cancers, so they readily develop lung cancer when given known lung carcinogens.

Vitamin A analogs called retinoids have been studied for several years as potential chemotherapeutic agents because they help regulate cell division, growth, differentiation and proliferation.
A new class of these vitamin A relatives has been created that includes Bexarotene.
These substances are called the rexinoids, so named because they are attracted to a molecule on cell surfaces called RXR.

Rexinoids tend to be much less toxic than retinoids, and among them Bexarotene has so far shown the most promise as a chemopreventive medicine. However, although it causes far fewer side effects, Bexarotene does have the effect of increasing blood lipid levels in many patients. Patients taking Bexarotene often need to take a drug to lower their cholesterol and triglyceride levels.

A new rexinoid called UAB30, just becoming available for laboratory studies, seems to have the potential to reduce even the high-lipid side effect.

" We will be testing this new compound, too, and if it turns out to be effective, these rexinoids will most likely become candidates for clinical trials in patients with precancerous nodules or bronchial dysplasia," a researcher says. " If the trials show reduction of cancers, I think these drugs may well become routinely used for lung cancer prevention." Prevention is considered vital to decreasing the impact of lung cancer, which accounts for 32 percent of cancer deaths in men and 25 percent of cancer deaths in women. The majority of lung cancer patients are not diagnosed until their cancer has reached an advanced stage, and current treatment regimens do not substantially improve the outcome for most of these patients.

Source: Washington University School of Medicine, 2006