**2.1 Epidemiology statistics**

Head and neck cancers refer to the carcinomas that originate from any parts of the upper aero-digestive tract. They also include the cancers of the thyroid and salivary glands. Although head and neck cancers no longer rank among the top 5 cancers in the latest report [1], they are still regarded as major types of cancer in Hong Kong [2]. One of the main reasons for this recognition is that nasopharyngeal cancer (NPC) is ranked sixth in terms of the number of new cases in the male population in Hong Kong [1]. The NPC worldwide figures illustrated by the age-standardized rate (ASR) was 1.2 per 100,000 [3], which were much lower than the incidence in Hong Kong which was 7.4 per 100,000 in the year 2012 [1]. The high incidence of NPC in Hong Kong is attributed to its special geographical epidemiology pattern that 76% of new cases were found in east and south-eastern parts of Asia, in which Hong Kong is situated [4]. Other head and neck cancers recorded in the Hong Kong Cancer Registry include cancers of the lip, oral cavity, pharynx, nasal cavity, middle ear and accessory sinuses, larynx, and thyroid gland. Altogether, there were 2617 new cases of head and neck cancers reported in 2016 in Hong Kong, which accounted for 8.3% of all cancer new cases [1]. NPC was the most common type of head and neck cancer, accounting for 46.6% of all new cases. It was followed by the cancer of the tongue and larynx which accounted for 13.9% and 11.4%, respectively [1]. Although there have been some variations in the trend of ASR between sub-sites, the overall ASR of head and neck cancers in Hong Kong has remained around 21 per 100,000 in the past decade. Because of the relatively high incidence of head and neck cancers, their treatment remains one of the major burdens in the health care services in Hong Kong [2].
