“…After the exclusion of irrelevant studies, a total of 28 studies were included. Among the remaining articles, four articles (Tandle et al, 2001 ; Jing et al, 2012 ; Saleem et al, 2013 ; Nagam et al, 2017 ) were not in agreement with HWE ( P < 0.001) and three duplicated data publications were further excluded (Ji et al, 2008 ; Misra et al, 2009 ; Wang et al, 2012 ). We included 21 case-control study involving 3,525 oral carcinoma patients and 3,712 controls (Summersgill et al, 2000 ; Drummond et al, 2002 ; Nagpal et al, 2002 ; Shen et al, 2002 ; Katiyar et al, 2003 ; Kietthubthew et al, 2003 ; Hsieh et al, 2005 ; Mitra et al, 2005 ; Bau et al, 2007 ; Kuroda et al, 2007 ; Chen et al, 2008 ; Lin et al, 2008 ; Tu et al, 2008 ; Kitkumthorn et al, 2010 ; Ihsan et al, 2011 ; Saini et al, 2011 ; Patel et al, 2013 ; Adduri et al, 2014 ; Sina et al, 2014 ; Rao et al, 2017 ; Zarate et al, 2017 ).…”