A link between smoking and breast cancer risk hasn't been clear. Many -- but not all -- studies have found that cigarette smoking increases breast cancer risk.
A very large research study strongly suggests that smoking for a long time dramatically increases breast cancer risk in women with a higher-than-average risk to begin with. The research was discussed with reporters and will be presented at the 2011 American Society of Clinical Oncology (ASCO) Annual Meeting.
Conducted during the 1990s, the Breast Cancer Prevention Trial included 13,338 women and was designed to see if treating women at high risk for breast cancer with tamoxifen could lower this risk. In 1998, the results showed that women at high risk who took tamoxifen were 50% less likely to have been diagnosed with breast cancer compared to women at high risk who didn't take tamoxifen. The women who didn't take tamoxifen took a placebo (sugar pill) that looked just like tamoxifen so no one knew who was taking what.
Because of the large drop in breast cancer risk in women who got tamoxifen, the study was stopped so women who weren't taking tamoxifen could start taking it if they wanted to.
The researchers also collected information on the women's lifestyle habits -- smoking, drinking alcohol, exercise intensity and frequency -- that doctors think might affect cancer risk, including breast, colon, lung, and uterine cancer risks.
The smoking statistics for the women in the study were:
- 55% never smoked
- 12% smoked for fewer than 15 years
- 25% smoked 15 to 35 years
- 8% smoked for 35 years or longer
During nearly 9 years of follow-up after the start of the study, the following number of women were diagnosed with cancer:
- 395 women with breast cancer
- 74 women with uterine cancer
- 66 women with lung cancer
- 35 women with colon cancer
The researchers then went back and looked at the smoking and cancer histories of the women at high risk to see if there was a link between smoking and cancer risk.
Overall, smoking increased the risk of breast, lung, and colon cancer in women at high risk.
Compared to women who never smoked, women who smoked between 15 and 35 years:
- were 34% more likely to be diagnosed with breast cancer
- were 5 times more likely to develop lung cancer if they smoked more than one pack of cigarettes per day
- were twice as likely to develop lung cancer if they smoked less than one pack per day
Compared to women who never smoked, women who smoked for 35 years or longer:
- were 59% more likely to be diagnosed with breast cancer
- were 30 times more likely to develop lung cancer if they smoked more than one pack of cigarettes per day
- were 13 times more likely to develop lung cancer if they smoked less than one pack per day
- were 5 times more likely to develop colon cancer
This research strongly suggests two things: smoking can dramatically increase breast cancer risk, and smoking is more risky for women with a higher-than-average risk of breast and other cancers.
No matter what your breast cancer risk, smoking can harm your health -- including breast health -- at any age. If you don't smoke, don't start. If you do smoke, find a program or system to help you quit. Quitting is tough, but it's definitely worth it. The American Lung Association offers a free online smoking cessation program. Local chapters of the American Cancer Society (ACS) offer the Fresh Start program to help people quit smoking. You can also call the ACS Quitline at 1-800-ACS-2345 to get support and free advice on how to stop smoking from trained counselors.