Epidemiology of the oral cancer

Abstract

Oral cancer is a malignant neoplasm that occurs in the oral cavity. Squamous cell carcinoma accounts for over 90% of the oral cancers in Japan, and others include adenocarcinoma derived from minor salivary gland, sarcoma, malignant lymphoma, and metastatic cancer. A number of cohort studies and case–control studies have been conducted as epidemiological technique to elucidate oral cancers. The number of oral cancer patients in Japan was 2,100 in 1975 and 6,900 in 2005 and further is estimated to be 10,000 patients by 2015, which is 1.6 times higher than the current number. Age-adjusted male-to- female ratio is 3:2, which is higher in males than in females, and the incidence of oral cancers decreases with the aging of the population in developed countries with the exception of Japan, in which the ratio is increasing. Of oral cancers, tongue carcinoma is the most common and accounts for 40% of oral cancers. The oral cavity, an entrance of the digestive system, is exposed to chemical stimuli such as smoking, drinking, and food as well as to mechanical stimuli including caries and ill-fitting prosthetic appliance and characterized by the existence of multiple circumstances in particular and risk factors associated with carcinogenesis. Examination of oral cancers can be easily conducted because these cancers can be confirmed directly by visual observation and palpation. The significance of oral cancer examination is early diagnosis and early treatment of not only oral cancers but also premalignant lesions, including leukoplakia and erythroplakia, and precancerous conditions, including lichen planus. It is reported that the detection rate of oral cancers and premalignant lesions is 0.99% in oral cancer screening and that the prevalence of precancerous lesions is 2.5 % in Japanese. Some patients with oral cancer may synchronously or metachronously develop double cancers. In patients with head and neck cancer including oral cancer, 60–70% of double cancers are found in the upper gastrointestinal tract or lung.