Women whose breast cancer spread to the lungs twice as likely to be smokers, says UC Davis study

(SACRAMENTO, Calif.) — Here’s one more reason for women to avoid smoking: breast cancer patients who smoke have a much higher risk of the disease spreading to their lungs than nonsmokers, says Susan Murin, an associate professor of medicine at the UC Davis School of Medicine and Medical Center. Her study and an editorial by two experts in the field appear in the June issue of the journal Chest.

Murin did a case control study of 87 UC Davis Cancer Center patients with invasive breast cancer that had spread to the lungs. She compared these women with 174 women with breast cancer that had not spread (metastasized). Each was matched by year of diagnosis, age at diagnosis, size of primary tumor and whether cancer was found in the lymph nodes.

Murin and John Inciardi, a UC Davis Medical Center statistician, found that women whose breast cancer had spread to the lungs were twice as likely to be smokers as women whose cancer had not metastasized. Breast cancer is the most common form of cancer in women, with more than 180,000 cases diagnosed annually. Caught early, five-year survival rates exceed 80 percent. But once it has spread to other parts of the body, it is much more difficult to treat.

Murin’s study supports previous research linking smoking to a higher risk of lung metastasis among women with breast cancer and with studies showing that women who smoke are more likely to die of breast cancer than nonsmokers, even though smoking is not a risk factor for breast cancer.

It’s an important distinction, said Murin, because while breast cancer is the most common cancer among women, lung cancer is the leading cause of cancer death among women.

“Women are in many ways more frightened of breast cancer than lung cancer, because it’s so much more common. Everyone knows someone who has breast cancer,” Murin said. “But women are more likely to survive breast cancer if they don’t smoke. If we can let them know that, it might motivate some women to quit.” The exact mechanism for spread is unclear, although Murin believes that cigarette smoke makes the lungs a more fertile environment for cancer.

“Smoking changes the immune function of the lungs and makes blood vessels more leaky,” she said. “Once cancer cells escape the bloodstream, they are more likely to set up housekeeping in distant sites.”

Still to be determined is whether other lifestyle factors might affect smoking, breast cancer and lung metastasis. “Smokers generally have less healthy diets and tend to exercise less than their nonsmoking counterparts,” said Murin. “We need to further study this relationship.”

Also in question is whether quitting smoking after breast cancer diagnosis limits this effect. Murin has received funding from the state Breast Cancer Research Program and the Tobacco-Related Diseases Program to examine the relationship of smoke exposure and lung metastasis in mice with breast tumors.

An accompanying editorial in Chest suggests that smokers who have been diagnosed with breast cancer should be offered support in quitting the habit.

Murin can be reached directly at 916-734-3564 or via e-mail at [email protected].

The American Cancer Society and the UC Davis Cancer Center funded this research.