Singapore, 15 December 2015 - Smoking is widely known as a key cause of lung cancer but the majority of lung cancer cases and deaths among Asian women occur in non-smokers . The predominant histological subtype of lung cancer in these women is adenocarcinoma, the subtype least influenced by smoking . Lung cancer in non-smokers remains one of the great puzzles of oncology, due to its high frequency and ethnic predominance in Asia. Lung cancer is the second leading cause of cancer deaths in women in Singapore, second only to breast cancer. In investigating this entity, researchers have speculated that female hormones may play a part in lung cancer.
- More than 28,000 women were involved in the study
- Childbirth lowers the risk of lung cancer in women
- Women who had their first menstrual cycle later than the age of 12 experienced higher risk of the lung adenocarcinoma subtype
Singapore researchers analysed records of more than 28,000 women, who participated in the Singapore Breast Cancer Screening Project (SBCSP) from October 1994 to February 1997, over 16 years and discovered evidence to show an inverse relationship between childbirth and risk of lung cancer.
Conducted by researchers from both the National University Singapore (NUS) Saw Swee Hock School of Public Health (SSHSPH) and National Cancer Centre Singapore (NCCS), the nation-wide study interviewed these women who were then between the ages of 50 and 64. Chinese women made up about 84 per cent of the study cohort and more than 93 per cent of the cohort was non-smokers. Subsequently, new diagnoses of lung cancer in this cohort over the next two decades were detected through the Singapore Cancer Registry.
The study showed that women who have given birth to at least one child will experience a 44 per cent lower risk of lung cancer as compared to those who have not. A total of 311 women developed lung cancer during the study period. Out of this cohort, 253 or 80 per cent of the cases occurred in non-smokers. Other reproductive factors, including age at menopause, reproductive period, age at first delivery, breastfeeding, oral contraceptives and hormone therapy, were not associated with risk.
Dr Tan Min-Han, co-author of the study, and Adjunct Assistant Professor at NUS SSHSPH and Visiting Consultant Medical Oncologist at NCCS, said, "In this large cohort study, having at least one child is associated with a substantial reduction in lung cancer risk for both smoking and non-smoking women. The lack of an association with reproductive period however points away from direct hormonal causes."
Another interesting point to note is that women, who have experienced their first menstrual cycle after the age of 16, were found to be twice as likely to be associated with the risk of having the lung adenocarcinoma subtype, as compared to those before the age of 12. These results contradict past studies which have reported an inverse relation but could be used as markers of nutritional status, though this relationship needs to be further evaluated in other well-designed studies that control for childhood and adult nutritional status.
Defence Minister Dr Ng Eng Hen, who then as a practising consultant surgeon had initiated the SBSCP, said, "I'm glad that medical researchers today are able to use this dataset that we set up more than 20 years ago as part of the Singapore Breast Cancer Screening Project. The fact that they could extend its use to correlate with lung cancer risks reflects their innovative and resourceful acumen. Congratulations to Dr Tan and his team for the publication of these findings in a prestigious international journal."
Additional researches integrating female hormonal factors such as estrogen and progesterone with female reproductive history will be required to further our understanding on factors that lead to the formation of lung cancer in women.
- Toh CK, Gao F, Lim W-T, Leong SS, Fong KW, Yao SO, et al. Never-smokers with lung cancer: epidemiologic evidence of a distinct disease entity. J Clin Oncol 2006; 24(15): 2245-51.
- Patel JD. Lung cancer in women. J Clin Oncol 2005; 23(14): 3212-3218.
Source: NUHS & NCCS