Dose–Response Relationship Between Cigarette Smoking and Site-Specific Cancer Risk
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Open Access Protocol BMJ Open: first published as 10.1136/bmjopen-2017-018930 on 1 November 2017. Downloaded from Dose–response relationship between cigarette smoking and site-specific cancer risk: protocol for a systematic review with an original design combining umbrella and traditional reviews Alessandra Lugo,1 Cristina Bosetti,2 Giulia Peveri,1 Matteo Rota,3 Vincenzo Bagnardi,4 Silvano Gallus1 To cite: Lugo A, Bosetti C, ABSTRACT Strengths and limitations of this study Peveri G, et al. Dose–response Introduction Only a limited number of meta-analyses relationship between cigarette providing risk curve functions of dose–response smoking and site-specific ► This study represents the most complete and relationships between various smoking-related variables cancer risk: protocol for a updated review on the association between cigarette and cancer-specific risk are available. systematic review with an smoking and site-specific cancer risk. Methods and analysis To identify all relevant original original design combining ► We will not conduct a systematic review of the entire umbrella and traditional publications on the issue, we will conduct a series of scientific literature on the issue, but we will rather reviews. BMJ Open comprehensive systematic reviews based on three use an original and innovative approach combining 2017;7:e018930. doi:10.1136/ subsequent literature searches: (1) an umbrella an umbrella review and traditional systematic bmjopen-2017-018930 review, to identify meta-analyses, pooled analyses and reviews. systematic reviews published before 28 April 2017 on ► Prepublication history and ► We will carry out dose–response analyses using additional material for this the association between cigarette smoking and the risk two-steps random-effects meta-regression models paper are available online. To of 28 (namely all) malignant neoplasms; (2) for each in order to examine potential non-linear relationships view these files, please visit cancer site, an updated review of original publications on between smoking-related variables and the risk of the journal online (http:// dx. doi. the association between cigarette smoking and cancer cancer. http://bmjopen.bmj.com/ org/ 10. 1136/ bmjopen- 2017- risk, starting from the last available comprehensive We will not systematically consider the assignment 018930). ► review identified through the umbrella review; and (3) a of a quality score to all original publications for each Received 1 August 2017 review of all original articles on the association between cancer site. Revised 1 September 2017 cigarette smoking and site-specific cancer risk included Accepted 18 September 2017 in the publications identified through the umbrella review and the updated reviews. The primary outcomes Trial registration number This protocol was registered of interest will be (1) the excess incidence/mortality in the International Prospective Register of Systematic of various cancers for smokers compared with never Reviews (CRD42017063991). smokers; and (2) the dose–response curves describing on October 1, 2021 by guest. Protected copyright. 1Department of Environmental the association between smoking intensity, duration and Health Sciences, IRCCS - Istituto time since stopping and incidence/mortality for various INTRODUCTION di Ricerche Farmacologiche cancers. For each cancer site, we will perform a meta- In 1950, Ernst Wynder and Evards Graham1 'Mario Negri', Milan, Italy analysis by pooling study-specific estimates for smoking 2 2Department of Oncology, and Richard Doll and Bradford Hill first status. We will also estimate the dose–response curves IRCCS - Istituto di Ricerche reported an association between tobacco Farmacologiche 'Mario Negri', for other smoking-related variables through random- smoking and lung cancer risk. Over the subse- Milan, Italy effects meta-regression models based on a non-linear quent 65 years, thousands of studies systemat- 3 Department of Biomedical and dose–response relationship framework. ically confirmed this association and found Clinical Sciences, Università Ethics and dissemination Ethics approval is not that tobacco smoking also increases the risk degli Studi di Milano, Milan, Italy required for this study. Main results will be published 3 4Department of Statistics and in peer-reviewed journals and will also be included in a of several other neoplasms. In 2004, tobacco Quantitative Methods, Università publicly available website. We will provide therefore the smoking has been classified as carcinogenic degli Studi di Milano-Bicocca, most complete and updated estimates on the association to humans (group 1) by the International Milan, Italy 3 between various measures of cigarette smoking and site- Agency for Research on Cancer (IARC), Correspondence to specific cancer risk. This will allow us to obtain precise which provided evidence on the causal rela- Dr. Alessandra Lugo; estimates on the cancer burden attributable to cigarette tionship between cigarette smoking and alessandra. lugo@ marionegri. it smoking. cancer of the lung, oral cavity, nasal cavity Lugo A, et al. BMJ Open 2017;7:e018930. doi:10.1136/bmjopen-2017-018930 1 Open Access BMJ Open: first published as 10.1136/bmjopen-2017-018930 on 1 November 2017. Downloaded from and paranasal sinuses, nasopharynx, oropharynx, hypo- 2. update of available cancer-specific reviews: for each pharynx, larynx, oesophagus, stomach, pancreas, liver, cancer site, the conduction of a systematic review of kidney, ureter, urinary bladder, cervix and myeloid studies providing original data (including pooled leukaemia.3 The results on the association between (ciga- analyses on individual participants’ data) on the asso- rette) smoking and other cancer sites, including cancers ciation between cigarette smoking and cancer-specific of the breast and endometrium, remain conflicting.3 risk, starting from the last available comprehensive Since the late 1980s, publications reporting results review publication identified through the umbrella from systematic reviews and meta-analyses, the large review (point 1); majority of which were unnecessary and misleading, 3. review of all original publications: a review of all rapidly increased.4 Although the effects of cigarette original articles on the association between cigarette smoking on cancer incidence and/or mortality have been smoking and site-specific cancer risk included in the largely investigated, only a limited number of systematic cancer-specific review publications identified through reviews/meta-analyses are available on the quantifica- the umbrella review (point 1) or identified through tion of the dose–response relationship between selected the update of the available reviews (point 2). smoking-related variables, including smoking intensity, The design of the present systematic reviews was devel- duration, pack-years and time since quitting, and the risk oped following the Preferred Reporting Items for System- of cancer. More importantly, just a few meta-analyses, if atic review and Meta-Analyses (PRISMA) guidelines12 and any, provided the cancer-specific risk curve functions of its extension for protocols (PRISMA-P).13 14 This protocol the dose–response relationships. Dose–response data, was registered in the International Prospective Register of however, are crucial to provide reliable and accurate Systematic Reviews on 4 May 2017 (registration number: estimates of the cancer burden due to smoking, both at CRD42017063991). individual level—absolute cancer incidence/mortality obtained through lung cancer risk assessment models Umbrella review and risk charts5 6; and at population level—smoking-at- Search strategy tributable deaths.7 8 Currently, the methods developed to We will conduct a systematic literature search to identify quantify cancer burden due to smoking use cancer-spe- all published meta-analyses, pooled analyses and system- cific estimates of relative risks (RR) according to tobacco atic reviews providing data on the association between smoking derived from a few large cohorts, mainly from cigarette smoking and the risk of various cancers. Litera- the USA.9 The use of these cohorts to derive RRs may ture search strategy will include combinations of medical lead to validity problems when applying these estimates subjects headings (MeSH) and text words related to to other populations with different smoking patterns.7 10 cancer and tobacco or smoking, and will be restricted to the Furthermore, these RRs are often estimated after allow- following publication types: meta-analyses, pooled anal- ance for a limited number of sociodemographic charac- yses and systematic reviews. No restriction on cancer site teristics, excluding potentially important confounding or on publication date will be applied. The following http://bmjopen.bmj.com/ variables, such as alcohol drinking. databases will be used: MEDLINE, Embase, Institute for Using an original and innovative approach, which Scientific Information (ISI) Web of Science (WoS) and combines an umbrella review11 and traditional system- Cochrane Database of Systematic Reviews (CDSR). The atic reviews, we aim at providing a comprehensive and search strings to be used in various databases are reported updated picture of the association between various smok- in (online supplementary appendix 1). To ensure liter- ing-related variables and the risk of all cancers. We will ature saturation, reference lists of selected relevant be able to estimate the most robust cancer-specific RRs, publications identified through the