ReviewHead and neck cancer among marijuana users: A meta-analysis of matched case–control studies
Introduction
Marijuana (Cannabis sativa) is a drug of vegetable origin that contains more than 60 compounds known as cannabinoids (Berthiller et al., 2009, Liang et al., 2009; Versteeg, Slot, van der Velden, & van der Weijden, 2008). The smoke generated by combustion of these compounds is recognized as a potential carcinogen (Rosenblatt, Darling, Chen, Sherman, & Schwartz, 2004). Cannabis affects cardiovascular, respiratory and immune systems, and a chronic use can cause premalignant changes with chance of developing into head and neck cancer (HNC) (Hashibe et al., 2005, Rosenblatt et al., 2004, Versteeg et al., 2008). The scientific literature to date has presented limited and conflicting data regarding the possible causal relationship of marijuana in the development of HNC (Aldington et al., 2008). There are several differences between these studies, including the criteria used for age, affected site, stage, and etiology, thus making it challenging to compare findings (Llewellyn, Linklater, Bell, Johnson, & Warnakulasuriya, 2004a). Previews publications are contradictory: some indicate that marijuana use increases the risk of developing HNC (Aldington et al., 2008, Feng et al., 2009), while others suggest that moderate marijuana use can have a protective effect (Liang et al., 2009). These differences may be related to methodological differences, target population, choice of controls, low response rate, sample size, and inefficiency in quantifying drug use.
A consortium of research groups on the epidemiology of HNC recently published a pooled analysis of five case–control studies (Berthiller et al., 2009). The results indicated that infrequent marijuana smoking does not confer increased risk of developing HNC. This study aimed to update the subject and conduct a systematic literature review and meta-analysis among nine case–control studies to answer the following question: Does marijuana use favor the development of HNC? Given the contradictory findings to date, it is important to assess studies with strong methodological consistency in order to develop a consensus on this question.
Section snippets
Search strategy and selection criteria
The following databases were used to search for original articles: The Cochrane Library, Pubmed, Lilacs, Embase, BBO, and Bireme SciELO. Articles published in English before July 2015 were included. This study was conducted according to the criteria of the PRISMA Statement guide to systematic reviews and meta-analysis (Moher, Liberati, Tetzlaff, & Altman, 2009).
The search strategy included keywords obtained from the Medical Subject Headings (MeSH). All possible combinations of the following
Search results
The search results are shown in the flow diagram of Fig. 1. The search revealed a total of 3558 publications in databases and duplicate articles were disregarded. Of these publications, 76 were selected for abstract review and 13 studies met the inclusion criteria for further assessment. After analysis, 3 articles were excluded for insufficient data (Dahlstrom et al., 2008, Gillison et al., 2008, Zhang et al., 2000) and 10 articles were selected for the systematic review (Aldington et al., 2008
Discussion
The result of this study indicated no association between lifetime marijuana use and the risk for development of HNC. Variables such as type, method, quantity, and frequency of use, age of onset, years of use, and cumulative use were investigated by studies but could not be included in the meta-analysis due to differences in the methods used. Smoking marijuana is the most common method for consuming cannabis, but it can also be taken orally, either directly or mixed with food. Nevertheless,
Conflict of interest
None.
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