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The enduring need for prospective cohort studies to more completely characterize the tobacco‐caused burden of cancer

In the mid-20th century before any causal associations between smoking of combustible tobacco cigarettes (henceforth referred to as “cigarettes”) and any disease had been established, case-control studies provided the first evidence from observational studies that cigarette smoking may be linked to cancer (eg, Refs. 1,2). At that time case-control studies were an unorthodox new study design, raising questions about the validity of this approach and hence how to properly interpret the strong statistical associations that had been observed between smoking and lung cancer. The need for data from cohort studies to augment the results of case-control studies was clear. Cohort studies such as the British Doctor's Study, American Cancer Society Cancer Prevention Study and US Veterans Study contributed essential additional evidence that reduced concerns about selection bias and information bias and established the temporal sequence by measuring smoking before cancer occurred, thus making a key contribution to the eventual conclusion that cigarette smoking was a cause of lung cancer (reviewed in Ref. 3). Additional research accumulated in the ensuing decades to document that cigarette smoking is a cause of numerous other malignancies, to the extent that an estimated 48% of all cancer deaths in the United States are attributable to cigarette smoking. With such an enormous body of evidence documenting the health consequences of cigarette smoking, it is possible to get lulled into thinking that investments in prospective cohort studies of cigarette smoking and cancer are no longer necessary. This is certainly not the case. The article authored by Weber and colleagues in this issue entitled “Cancer incidence and cancer death in relation to tobacco smoking in a population-based Australian cohort study” provides an excellent example of why contemporary prospective cohort studies remain vital. This report, based on the 45 and Up Study, addresses the familiar topic of cigarette smoking and cancer, but with features that add important evidence on the topic. The 45 and Up Study is a prospective cohort study of approximately 229 000 people in Australia, a nation-continent that has been underrepresented in largescale cohort studies on this topic. The study's baseline data collection took place in 2006-2009. A cohort assembled this recently has advantages for characterizing the magnitude of the associations between cigarette smoking and cancer in the modern era. Thus, the major novelty of this report does not lie in the study questions addressed, but rather that the study was carried out in a new place and during modern times. There are at least four strong reasons that prospective cohort studies such as the 45 and Up Study that are from new geographic locations and/or carried out in the modern era are particularly valuable: