Trends in the incidence of oral cancer in Nova Scotia from 1983 to 1997.

OBJECTIVE

The purpose of the study was to characterize the total burden of oral cancer in Nova Scotia over the 15-year period from 1983 to 1997 and to identify any trends in the number of cases or incidence rates at specific anatomic sites or within specific age or sex groups over this time period.

STUDY DESIGN

All cases that had a diagnosis of invasive oral cancer (ICD-9 sites 140-146) during the study period were retrieved from the records of the Nova Scotia Cancer Registry, which theoretically includes all cancer cases in the province. Cases of in situ carcinoma, lymphoma, and leukemia were not included. All cases during the study period were categorized by tumor site and the age and sex of the patient. Tumors at ICD-9 sites 141 and 143-146 were analyzed separately as intraoral cancer. Trends were studied by grouping cases into three 5-year periods: period 1 (1983-1987), period 2 (1988-1992), and period 3 (1993-1997). Age-standardized incidence rates were calculated to the 1991 Canadian standard population.

RESULTS

A total of 1,155 cases of oral cancer were registered in Nova Scotia for this 15-year study period, accounting for 2.0% of all cancer cases. There was an average of 57 cases in men and 20 cases in women per year. Overall, the most common site was the lip (26% of cases), followed by the tongue (20%), other mouth (16%), tonsil/oropharynx (12%), salivary gland (12%), floor of mouth (10%), and gum (4%). About 5% of cases occurred in patients 40 years and younger, and 53% occurred in patients 65 years and older. Lip cancer in men decreased by 38%, and the age-standardized incidence rate fell from 5.6 to 3.0 per 100,000 from period 1 to period 3. Intraoral cancers in men increased by 23% and the age-standardized incidence rate increased by 10% from period 1 to period 3. Both measures peaked in period 2. Intraoral cancer in women increased steadily by 84%, and the age-standardized incidence rate increased by 48% from period 1 to 3. The male-to-female ratio for intraoral cancer cases decreased from 2.9 to 2.5 to 1.9 over the 3 periods.

CONCLUSION

Although there was a decreasing trend for lip cancer, the number of cases and the age-standardized incidence rate for intraoral cancer increased over the 15-year study period. Intraoral cancer increases in females were dramatic. Trends in the number of cases reflected changing risk and a growing, aging population. More oral cancers occurred each year than cancers of the uterine cervix, suggesting the need for more resource allocation in the areas of research, prevention, and early detection of oral cancer.