Colon cancer is one of the five most common cancers in men and women in the United States and is also one of the country's leading causes of cancer death. According to the American Cancer Society, an estimated 135,400 people were diagnosed with colon cancer in the United States in 2017, and a little more than 50,260 people succumbed to the disease. One in 22 men and one in 24 women will be diagnosed with colon cancer in their lifetime.
People are used to talking about its potential causes: too much fat, too little fiber, even a rogue gene that can lead to cancer as young as a patient's teens. Now doctors at Johns Hopkins in Baltimore are proposing a new, complementary theory: Many cancers may be traceable to two specific digestive bacteria that form a film on the colon, raising the prospect that some high-risk patients might one day be identified with a simple, painless stool test.
The paper, published last month in the journal Science, says these bacteria invade the protective mucous layer of the colon and create a small ecosystem, including nutrients the bacteria need to survive, causing chronic inflammation and subsequent DNA damage that supports tumor formation.
"It was quite a surprise to find predominantly two bacteria between a [healthy] colon and a precancerous polyp," said Cynthia Sears, an infectious-disease specialist at Johns Hopkins who led the study.
The Hopkins team found these two bacteria — out of more than 500 different classes of bacteria in people's colons and more than a trillion individual bugs in your gut — in patients whose cancers are linked to a genetic syndrome called familial adenomatous polyposis, or FAP.