Cigarette smoking and cervical cancer in Sydney, Australia 1980 - 1983: A case-control study

Abstract

The purpose of these hospital and community-based case-control studies was to investigate the association between cigarette smoking and cervical cancer (in-situ and invasive). A number of local and international studies have investigated the association between cigarette smoking and cervical cancer. However few if any have investigated this association in in-situ and invasive cervical cancer using community and hospital controls at the same time. The association between cigarette smoking and cervical cancer is investigated in samples of 114 in-situ cervical cancer cases, 75 invasive cervical cancer cases, 181 community controls and 331 hospital controls. These cervical cancer cases and hospital controls were collected from Royal Price Alfred hospital and Westmead hospital in Sydney, Australia during 1980 - 1983. Community control data were identified from the files of the family doctor or from university affiliated general practices from the same areas as the in-situ cases. The data for invasive cases and hospital controls were collected as a part of a WHO Collaborative Study of Neoplasia and Steroid Contraceptives in Australia (1980-1983). The data for in-situ cases and community controls were collected as part of a case-control study on dietary factors and risk of in-situ cervical cancer conducted by Brock and others (1980-1983). Number of sexual partners, induced abortion experience, practise of "safe period" contraception, and cigarette smoking measured both by ever smoked and number of cigarettes smoked per day are significantly associated with increased risk of developing in-situ cervical cancer using community controls. For in-situ cervical cancer cases using hospital controls number of sexual partners, early age at first intercourse, spouses' duration of education, induced abortion experience, spirit drinking habit, use of oral contraceptives and smoking status are identified as risk factors. Invasive cervical cancer using hospital controls revealed a different pattern of risk factors. In this study parous women, women who engaged in unskilled jobs, women who drank beer and women who smoked are at an increased risk of developing invasive cervical cancer. Thus in this study cigarette smoking is established as one of risk factors for cervical cancer. The increased risks of developing cervical cancer caused by cigarette smoking are various. For in-situ cervical cancer using community and hospital controls the risks are 2.3 and 1.8 respectively; for invasive cervical cancer the risk is 1.8. A dose response relationship between number of cigarettes smoked per day and increased risk of developing in-situ cervical cancer was also observed in the study involving in-situ cervical cancer using community controls. The study on in-situ cervical cancer with different control groups namely hospital and community controls revealed a different pattern with regard to the risk factors. It is still uncertain whether this difference is a true difference with regard to different exposure toward the hospital and community populations or as the result of biases including selection bias, admission bias, information bias and recall bias. With regard to the smoking variables, the finding in this study is still inconclusive since this study was not specifically designed to investigate the association between cigarette smoking and cervical cancer and also this study failed to control for another major risk factor for cervical cancer, namely history of infection of Human Papilloma Virus. Thus in order to establish cigarette smoking as a risk factor for cervical cancer it is still necessary to further investigate the history of Human Papilloma Virus infection in this study population.