Background: Shifts in the distribution of histologic types have reportedly accompanied changes in lung carcinoma incidence in the last two decades. In the United States, incidence rates of squamous cell and small cell carcinoma have been showing a decline in males, after peaks in 1981-82 and 1986-87, respectively; however, no decline has been observed in females. In both genders, adenocarcinoma incidence is increasing. The authors evaluated lung carcinoma incidence rates in two Swiss cantons for changes in trends by gender, birth cohort, and histologic type.
Methods: The authors analyzed data on population-based lung carcinoma incidence from the Swiss cantons of Vaud and Neuchatel (the populations of which total about 760,000). Cancers were grouped into four major histologic types. The proportion of cancers not histologically confirmed was approximately 8% across the entire study period. Incidence rates were age-standardized on the basis of the world standard population.
Results: Overall, of 7423 cancer cases diagnosed in the period 1974-1994, squamous cell carcinomas accounted for 37%, small cell carcinomas and adenocarcinomas 18% each, and other carcinomas 16%. Rates of squamous cell and small cell carcinoma incidence in males of all ages dropped in the last quinquennium, while corresponding rates in females increased steadily. Conversely, adenocarcinoma incidence increased in both genders by approximately 2.5-fold; and during the period 1990-1994, in young adults of both genders, it was more than 3-fold higher than the incidence of squamous cell carcinoma. At variance with squamous cell carcinoma, the incidence of which reached its peaks in the 1910-20 birth cohorts in males and in the 1930-40 birth cohorts in females, adenocarcinoma revealed a similar birth cohort pattern in the two genders, with still no sign of decline.
Conclusions: Although changes in diagnostic practices may have played a role, the incidence data presented in this study suggest that adenocarcinoma is sustaining a new lung carcinoma epidemic, chiefly attributable to the switch to low-tar, filtered cigarettes. Its pattern seems remarkably similar in the two genders. Thus, the authors conclude that similar exposure to tobacco-related carcinogens leads to similar rates of histologic type-specific lung carcinoma incidence in males and females.