Oral cancer in South Australia : a twenty year study 1977-1996

Abstract

Oral cancer comprises a group of malignancies involving the tissues of the lips and oral cavity. Oral cancer is common in humans and is consistently reported as being among the ten most frequently occurring cancers (Parkin et al 1993). There have been recent reports that the mortality from this form of cancer is increasing (Macfarlane et at 7994a; Zheng et at 1999; Su et al 1999). Globally, there is considerable geographic variation in the overall incidence of oral cancer. In most Western countries oral cancer accounts for less than 5Vo of all cancer cases, whereas in India it has been reported that up to 4OVo of al malignancies occur in the oral cavity' The pattern of oral cancer in South Australia has not been examined in any detail for over 15 years (Roder and Wilson 1983). The purpose of this study was to carry out a review of the epidemiology of oral cancer in South Australia from 191'7-1996. Baseline epidemiological data for this study were provided by the Central Cancer Registry Unit of the Epidemiology branch of the South Australian Health Commission. This population-based cancer registry was established in 1977 and collects cancer data for the state of South Australia. Statutory cancer registration procedures enacted in 1976 mean all new cases of oral cancer are notified to the registry. Population statistics are also available from the Australian Bureau of Statistics. These data were analysed to give population-based incidence and mortality rates and trends over the 20-year period. A total of 4054 cases of oral cancer were reported to the South Australian Cancer Registry between l977-1996. Of these cases, 2956 (72.9%) occurred in males while l098 (27.1%) occurred in females. The vast majority of oral malignancies were squamous cell carcinomas (88.0%) and there was an increasing incidence with age. The average age at diagnosis for oral cancer was 59.3 years in males and 66.0 years in females. The most common site of occurrence was the lip (2716 cases, 67.0%), followed by the tongue (454 cases , 11.2%), major salivary glands (302 cases, 7.4%), other and unspecified parts of the mouth (286 cases,7.1%), floor of the mouth (226 cases, 5.6%) and the gum (70 cases, 1.7%). Population-based incidence rates in both sexes showed that the overall "oral cancer" rates were dominated by lip cancer. There was a statistically significant increase in the incidence of lip cancer in South Australia over the 20-year period in both sexes. In males this appears to have plateaued in the past decade, although in females it continues to increase. Incidence rates for the other sites are quite low and stable in both sexes. Mortality rates for oral cancer in this state are low and stable. The study also reviews the epidemiology of oral cancer in South Australia from a global perspective. It shows that although the incidence of cancer in the intraoral and salivary gland sites are relatively low in global terms, lip cancer incidence in South Australia is amongst the highest in the world in both sexes. The rapid and sustained increases seen in females, is an area of particular concern. This study also highlights the importance of clearly defining the term "oral cancer" and the importance of analysing trends at each individual site rather than just considering oral cancer in its totality.