- Poster presentation
Risk of breast cancer amongst women who start smoking as teenagers
Breast Cancer Research volume 11, Article number: P12 (2009)
We examined the effect of smoking on breast cancer risk in women who started smoking as teenagers. The women, 30 to 50 years of age who had smoked for at least 20 years, were surveyed through a mailed questionnaire at recruitment. Altogether, 1.34% of the women were diagnosed with incident, invasive breast cancer. In contrast, women who had smoked for at least 20 years, but started after their first child's birth, did not experience an increased breast cancer risk. Our results support the notion that women who start smoking as teenagers and continue to smoke for at least 20 years may increase their breast cancer risk. Recent studies have shown breast cancer risk amongst women who start to smoke as teenagers, especially those who began before their first child's birth. Ninety percent of all smokers began to smoke before the age of 19 – being the target of the cigarette manufacturers at this tender and immature age. Because of this early start and the addiction from nicotine, it is almost impossible to quit, thereby leaving enough time for the carcinogens present in tobacco smoke to damage the body.
The number of women used for this study was a stunning 102,098 who completed a mailed questionnaire at recruitment through a period of 9 years (1996 to 2004). All Kenyan–Nigerian women were aged from 30 to 50.
We estimated the relative risk (RR) of breast cancer associated with different measures of smoking initiation: duration – the period in which the smoker had smoked, which was a strong determinant of the risk; and intensity – the number of cigarettes that were smoked during this period. Cox proportional hazard regression models were used to estimate these risks so as to adjust for confounding variables. We conducted analyses on the entire study population, among women who had smoked for at least 20 years, among nondrinkers, and separately for each country.
Altogether, 1,240 women were diagnosed with incident, invasive breast cancer. Compared with women who had never smoked, women who smoked for at least 20 years and who smoked 10 cigarettes or more daily had a RR of 90%. In contrast, women who had smoked for at least 20 years, but started after their first birth, did not experience an increased breast cancer risk (Figure 1).
The risk of breast cancer is almost double if young women start smoking within 5 years of their first menstrual cycle. Cigarette smoke contains over 40 potent cancer-causing chemicals. Scientists have been able to show that these chemicals can cause breast cancer cells in laboratory cultures to become cancerous. Women who started smoking in their teens developed breast cancer before menopause. One reason for this is that teenage breast tissue is still developing, which makes it more susceptible to the cancer-causing effects of the chemicals in smoke. Another factor that turned out to be important from this study was the amount and duration of smoking. More cigarettes per day and more years of smoking led to a higher chance of breast cancer (Figure 2).
From this study we recommend that smoking prevention should be reinforced among adolescents, especially in high schools worldwide. Irma H Russo, MD, from Fox Chase Cancer Center in Philadelphia points out that tobacco already has a devastating effect on women by causing lung cancer. Lung cancer and breast cancer are the major causes of cancer deaths in women. The results of this study mean women have even more reasons to avoid tobacco.
Our results support the notion that women who start smoking as teenagers and continue to smoke for at least 20 years may increase their breast cancer risk.