Smoking, The Missing Drug Interaction in Clinical Trials: Ignoring the Obvious

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Abstract
Tobacco use is universally recognized as the foremost preventable cause of cancer in the United States and globally and is responsible for 30% of all cancer-related deaths in the United States. Tobacco use, including exposure to secondhand smoke has been implicated as a causal or contributory agent in an ever-expanding list of cancers, including lung, oral cavity and pharynx, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix, and myeloid leukemia. In addition to and independent of the etiologic effects of tobacco carcinogens in numerous cancers, there is a growing literature on the direct and indirect effects of smoking on treatment efficacy (short-term and long-term outcomes), toxicity and morbidity, quality of life (QOL), recurrence, second primary tumors (SPT), and survival time as summarized below. Oncology health professionals have called for increased advocacy for tobacco control. Despite the critical relevance of smoking to cancer outcomes, most oncology clinical trials do not collect data on smoking history and status unless the malignancy is widely acknowledged as smoking related (e.g., lung or head and neck cancer). Usually, these data are collected only at trial registration. Changes in smoking status during treatment or follow-up are monitored in very few trials and are infrequently reported in sample descriptions or included in analysis plans as a potential moderator of outcomes. Based on mounting evidence that tobacco use affects cancer treatment outcomes and survival, we recommend that smoking history and status be systematically collected as core data in all oncology clinical trials: at diagnosis, at trial registration, and throughout treatment and follow-up to long-term survival or death. We feel that the inclusion and analysis of such data in clinical trials will add important information to the interpretation of outcomes and the development of scientific knowledge in this area. Smoking status has been called another “vital sign” because of its relevance to a patient's immediate medical condition. We explain the critical value of knowing the smoking status of every patient with cancer at every visit by providing a brief overview of the following research findings: (a) the effects of tobacco use on cancer treatment and outcome; (b) recent findings on the role of nicotine in malignant processes; (c) some unexpected results concerning tobacco status, treatment, and disease outcome; and (d) identifying key questions that remain to be addressed. We provide a suggested set of items for inclusion in clinical trial data sets that also are useful in clinical practice.