Bacteria and Viruses
Gut bacteria can alter cancer risk up or down
“Gone are the days of one organism, one disease. We’re really looking at how a whole community of microbes influences disease risk, ” Hullar said. “For example, scientists are looking at how the metabolism of the microbiome — all of the members of the microbial community — influences its host, ” she said. Researchers are exploring questions such as whether the microbiome produces metabolites that promote tumor growth or may prevent cancer.
There are several different types of human bacteria that can directly fuel colorectal cancer risk, Hullar said. Those include the bacterial species Streptococcus gallolyticus and Fusobacterium nucleatum, as well as certain types of E. coli and conglomerate communities of bacteria that form layers in the gut that are called biofilms. All of these microbes act in different ways on the cells that line our gut to increase risk of tumor formation, she said.
But interestingly, many other types of gut bacteria can alter cancer risk — either up or down — through indirect routes that involve what we eat.
Because these bacteria help digest our food, what we eat influences what they excrete in our gut. Some microbial byproducts — such as those produced when processed meat or high-protein foods are digested — increase cancer risk. Compounds formed in the gut by bacteria during the digestion of a high-fiber food — for example, cruciferous vegetables such as broccoli — seem to be linked to a lower risk of colorectal cancer, Hullar said. She and her colleagues are studying the different microbial communities in people with high or low levels of one of those compounds linked to a lower risk of cancer, known as enterolignans. They are now researching whether changing people’s diets changes the amount of enterolignans they produce and how the human cells that line the gut may respond to those compounds in cancer prevention.
Two deadly pathogens
Although these complex bacterial communities seem to have equally complex relationships with cancer risk, there’s at least one bacterium whose link to cancer is somewhat more straightforward. The bacterium Helicobacter pylori — which colonizes in the stomachs of about two thirds of people worldwide — is directly linked to stomach cancer, the fifth most common cancer in the world and the third most common cause of cancer-related death, said microbiologist Dr. Meira Epplein of Vanderbilt University at Monday’s session.
Although eradicating the bacterium may stem stomach cancer, it’s not yet clear who should be targeted, Epplein said. Her team is studying communities in the Southeastern U.S. who have higher than average levels of H. pylori infection.
But even here, the picture is nuanced. Most people infected with the bacterium don’t develop stomach cancer, and H. pylori infection also seems to reduce the risk of a type of esophageal cancer, Epplein said, so more research is needed.
Stopping hepatitis C from turning deadly
Dr. Lesley Miller of Emory University dropped a statistic that she felt hasn’t reached enough of the public — that hepatitis C virus kills more people in the U.S. than any other infectious disease, including HIV. Up to 4 million people in the U.S. are infected with the virus, Miller said, and it’s incredibly deadly. If unchecked, it can lead to cirrhosis and liver cancer, which is very difficult to treat.
But the infection is very treatable if diagnosed early enough, she said. And in 2012, the Centers for Disease Control and Prevention recommended that all baby boomers, the segment of the population that has the most hepatitis-C infections, be screened for the virus. The infection can be cleared with a simple (if expensive) course of oral antivirals before it progresses to cancer.
“It’s really frustrating to see a case of cancer that’s completely preventable, if we could have caught the infection and treated it earlier, ” Miller said.
HPV vaccine: some good news, some bad news
Public health researchers from around the country convened at Monday’s meeting to present their latest findings on the HPV vaccine — who’s getting it, who’s not, do parents who decline the vaccine for their children ever change their minds, and is the vaccine doing any good?
The HPV vaccine may be one of the best cancer prevention methods to come onto the market in the past few decades. It’s highly effective at preventing the strains of HPV that cause nearly all cases of cervical cancer and many other anogenital cancers — plus head and neck cancers. The vaccine, which was approved for girls in 2006 and for boys in 2009, works best if people are vaccinated before they’re exposed to the virus. Since HPV is sexually transmitted, that means the vaccine is recommended for pre-adolescent children aged 11-12 — before they’re sexually active. The vaccine is also approved for teenagers and young adults in the U.S. up to age 26. (Children under 14 need just two doses of the vaccine; those 15 and older still need three doses.)
And in countries where most kids get the vaccine, it’s working. In Australia, which has a nationwide vaccination program, cases of genital warts, an earlier sign of HPV infection than the virus-linked cancers, dropped more than 90 percent in young women after the vaccine was implemented. But clinicians and researchers alike have been dismayed by the vaccine’s low uptake rate in the U.S. In 2015, only 42 percent of girls and 28 percent of boys had received the full vaccine series.
Many researchers are trying to boost that number, including some who presented Monday at ASPO.
But the results of their efforts have not always been so easy to understand, they said. Dr. Nora Henrikson of Kaiser Permanente Washington Health Research Institute (formerly the Group Health Research Institute) in Seattle presented results from a study in which parents of unvaccinated children aged 10 and older received a letter with information about the vaccine written by a pediatrician and nurse. Starting when the children turned 11 and were eligible for the vaccine, they also got automated phone call reminders and the option to opt in to a text-reminder system.
Overall, the Kaiser study found a slight boost to vaccine rates, Henrikson said. In surveys, the parents said they liked the mailed information, and 23 percent of those who received a letter and phone-call reminder brought their child in for the first vaccine dose within three months of the reminder, as compared to 18 percent of parents who didn’t get a phone or mail prompt.
Parents with young adolescents who haven’t yet gotten their kids vaccinated aren’t necessarily going to be lifelong vaccine refusers, as Henrikson’s study found. That squares with a study led by Dr. Melanie Kornides from Harvard Medical School, who asked: Do parents who actively refuse the HPV vaccine for their children ever change their minds? Using an online survey, she and her colleagues looked at close to 500 parents of adolescents who were eligible and had access to the HPV vaccine and had refused the vaccine at a well-child checkup. Surprisingly, 45 percent of those parents later changed their mind and said yes to the vaccine. Another 24 percent said they were planning to get their child vaccinated in the coming year.
