A new survey conducted by the National Center for Sexual Health Promotion at Indiana University has found that well over half of sexually active teens in the United States regularly use condoms when they have intercourse, a percentage much higher than that for sexually active adults. The survey, reported in today’s New York Times (link) and set to appear in the Journal of Sexual Medicine, could be good news in the battle against cancers linked to sexually transmitted infections, if the trend in safer sexual practices is robust and continues into the future.
Although not well known by most people, infections play an important role in the development of some cancers. Worldwide, approximately 15 percent of all cancers have been linked to infections. In developing countries, this number reaches almost 25 percent.
Certain infections can either directly or indirectly cause changes that can lead to cancer. This can happen because of the chronic inflammation that some infections cause or by an infectious agent (like a virus) changing the behavior of infected cells. Infections that compromise the immune system (like HIV) also increase cancer risk by making the body less able to defend against infections that can cause cancer.
Not surprisingly, infection-associated cancers are not a health burden borne equally by all. The poor living conditions and inadequate health care experienced by many people worldwide increase the likelihood of cancer resulting from chronic infections.There are at least ten infectious agents that are known to increase the risk of cancer (see table), and several of them are quite common. Yet, in most instances, only a small proportion of those infected actually go on to develop cancer because it takes a unique set of factors along with the infection to turn normal cells cancerous.
Still, these infectious agents have a substantial impact on cancer worldwide. Of particular importance are human papillomavirus (HPV), hepatitis B and C viruses, and Helicobacter pylori. HPV is a sexually transmitted virus that is linked to numerous cancers, with cervical cancer being the most important. It’s estimated that almost all cervical cancers are caused by HPV infection. Hepatitis B and C infect the liver and together account for the large majority of liver cancer. Finally, Helicobacter pylori, a bacteria that infects the stomach, has been estimated to cause upwards of 75 percent of all stomach cancers, the second most common cancer worldwide.
The promise of prevention is a bright spot when looking at the reach of infection-associated cancers. To lower their risk, individuals can take concrete steps like avoiding blood exposure (by not sharing needles, for example), practicing safer sex and, for women, getting regular Pap tests (which test for cervical cancer). There is also very strong evidence that vaccinating girls (around age 11 or 12) against HPV can greatly reduce the risk of cervical cancer later in life . Growing use of the hepatitis B vaccine worldwide is expected to result in similar benefits in liver cancer. Advances on vaccines for other agents also offer much hope for prevention.