[1] Univ Malaya, Fac Med, Dept Social & Prevent Med, Julius Ctr Univ Malaya, Kuala Lumpur 50603, Malaysia
[2] Univ Malaya, Dept Surg, Fac Med, Kuala Lumpur 50603, Malaysia
[3] Univ Malaya, Canc Res Inst, Kuala Lumpur 50603, Malaysia
[4] Univ Bristol, Sch Social & Community Med, Acad Unit Surg Res, Bristol, Avon, England
[5] Univ Hosp Bristol NHS Fdn Trust, Div Head & Neck Surg, Bristol, Avon, England
[6] Univ Kebangsaan Malaysia, UKM Med Ctr, Kuala Lumpur 56000, Malaysia
[7] Hosp Tuanku Jaafar, Dept Surg, Seremban 70300, Negeri Sembilan, Malaysia