The almond-shaped lump on Brian Hill's throat didn't make sense to him. The doctor said it was a symptom of advanced oral cancer, but Hill had never smoked a cigarette or chewed a plug of tobacco, considered the main causes of the disease, when he was diagnosed in 1997. So why was it there? Not until four years later did Hill get an explanation for his brush with death: a microbe called human papilloma virus-16 (HPV-16) had apparently moved into his tonsils, gradually turning normal cells into cancer. Hill, now 59, had become part of a wave of relatively young nonsmokers who contracted oral cancer from the sexually transmitted virus, fueling an overall increase in new cases.
Viruses such as human papilloma may be the most overlooked bad guys in the war on cancer, silent invaders that contribute to more than a dozen malignancies and may cause 15 percent of the cancer cases worldwide each year.
"What we know about HPV-16 as a cancer causer is just the tip of the iceberg," said Hill, founder of the Oral Cancer Foundation, which funds research for a disease that strikes 34,000 Americans annually and is caused by the same virus that can lead to cancers of the cervix, vulva, anus, and penis.
The cancer toll from germs - both viruses and bacteria - may turn out to be higher as researchers discover more of these elusive microbes and how they do their grim work. Currently, scientists can't even estimate how many viruses afflict human beings, let alone how they impact human health. Some suspect that unknown viruses may be causing cancers that are now blamed on something else, much the way doctors believed that stress and spicy foods caused stomach ulcers until scientists discovered the real culprit - bacteria - in 1982.
"There are a lot of infectious diseases that we just don't know about, including a lot of cancers," said Matthew Meyerson, a cancer genetics researcher at the Dana-Farber Cancer Institute in Boston and the Broad Institute of Cambridge. Unfortunately, he said scientists have not come up with a simple way to identify unknown viruses lurking inside human genes.
But it's already clear that cancer is more contagious than most people realize: Everyday acts of intimacy such as kissing and lovemaking potentially transmit viruses from one person to the next. For an unlucky minority, those viruses will cause cancer years later as the genetic damage to cells slowly mounts. For instance, people who have oral sex with six or more partners triple their risk of developing oral cancer due to the transmission of the papilloma virus, according to a recent study from Johns Hopkins University in Baltimore.
Yet, medical advice on how to prevent cancer usually centers on avoiding tobacco, sunlight, cancer-causing foods and environmental pollution, with only secondary mention of the need for protection against infections by cancer-causing viruses.
"We worry about 'Should I eat those french fries or that apple?' but we don't manage our infections. I don't say, 'I think I'll have a little less Epstein-Barr virus today,'" said Julie Parsonnet, a researcher at Stanford Comprehensive Cancer Center in California who focuses on infectious diseases. "We are probably focusing on the wrong thing."
Ultimately, Parsonnet believes that infections from viruses and bacteria combined account for at least a quarter of cancers and more in developing countries where untreated infections are more common.