BIOLOGICAL AGENTS

Although several biological agents have been linked convincingly with increased risks for cancer in humans, only infection of the lower fema le genital tract with human papillomavirus (HPV) and colonization of t he gastrointestinal tract viith Helicobacter pylori are of importance for cancer occurrence in the Nordic countries. HPV types 16 and 18, an d probably types 31 and 33, are causally linked with cervical cancer a nd H. pylori, a Gram-negative bacteria, with gastric cancer. The estim ated prevalence of genital infections with oncogenic types of HPV amon g Nordic women and the associated risk estimates indicate that approxi mately 45% of all cervical cancers arising in the Nordic countries are caused by such infections. This will be equivalent to about 550 cases in these countries each year around 2000, or 1% of all cancers arisin g in these populations. Similarly, the 35% prevalence of persistent ga stric infection with H. pylori in the adult Nordic population and the associated risk estimates indicate that some 58% of all gastric cancer s in the Nordic countries are due to this bacteria. This will correspo nd to about 2,350 new cases annually around the year 2000, with 1,350 among men and 1,000 among women, or approximately 2% of all cancers ar ising in the Nordic population.