Recently Parkin et al. (1999) made estimates of the global health burden of infection-associated cancers. Their conclusions were that approximately 15% of human neoplasms were caused by infectious agents worldwide as of 1990. This includes 10% of all lymphomas and leukemias, 70% of all liver cancers, 42% of gastric carcinomas, and 88% of carcinomas of the cervix and vulva worldwide. These authors estimated that 1.2 million cancer cases were attributable to infectious agents in the year 1990. Most of this burden was related to viral infections. Almost a third, 4.3% of the 14.8%, were related to infection with Helicobacter but only a small pro- portion to parasitic infections. Theoretically, with the development of appropriate vaccines and other therapeutic modalities, most such cancers could probably be prevented within the
next decade, given the appropriate economic requirements. Just two decades ago, the percent- age of cancers caused by infectious agents was considered to be less than 1%; but as our knowledge has increased, infectious agents clearly play a significant role in the worldwide burden of cancer.