The most important object at Imperial College London this week was a plastic cup that costs about nine cents. Inside the cup was saliva. The saliva, it turns out, had been talking.
Researchers at Imperial, working with the Royal Marsden hospital and funded by Pancreatic Cancer UK, are building a test that reads the bacteria in a patient’s mouth to predict how a pancreatic tumor will respond to chemotherapy. The lead investigator described the award as a chance to bring microbiome science into the mainstream of cancer research and to reframe how doctors predict who benefits from treatment. Advanced pancreatic cancer responds to the best current chemotherapy in barely three patients in ten. The cup is being asked to change that arithmetic.
I spent Tuesday with Dr. Emmett Cressler, who directs a clinical microbiome lab in the American Midwest and who has, over three decades, become very friendly with the human mouth.
“The mouth has never been neutral,” Dr. Cressler told me, in his office, in front of a shelf of labeled specimen containers, which he declined to move. “A mouth is a witness. For fifty thousand years it has been testifying. We simply never handed it a microphone. What London is doing is handing it the microphone.”
His lab’s protocol fits on an index card. A patient spits in a cup. That is the entire patient contribution. The bacteria in the sample are counted, sorted, and read like a ledger, because bacterial populations in the mouth shift in step with disease elsewhere in the body — the pancreas included, in the studies now converging on this question.
“Some people hear ‘bacteria’ and think informant,” he said. “Wrong word. A bacterium isn’t informing on you. A bacterium is living in your apartment, and it leaves a review of the building on its way out. The review is accurate. The review is about the building. Your dentist has been reading these reviews for years without telling anyone.”
The scientific excitement is not that saliva is new — dentists, archaeologists, and paternity lawyers have known for decades that spit carries information. The excitement is that a cheap, painless cup could sit at the front of the cancer pipeline, screening and sorting before anyone orders a scan. Cups do not need contrast dye. Cups do not have waiting lists. A cup can be mailed.
Dr. Cressler walked me through the specimen cooler in his lobby, forty cups from a single morning’s clinic, each one labeled with a number. He looked at the cooler the way a librarian looks at a new wing.
“Every one of those cups contains a crowd,” he said. “Billions of residents, and their census just arrived. We used to think the pancreas kept its books in a locked room. It turns out the books were at the front desk the whole time, and the front desk has been making copies into your coffee mug since you were a child.”
He asked how long I had been carrying my own crowd. “Fifty-one years,” he said. “Mine has opinions about the coffee.”
The Imperial team will enroll patients, sequence their saliva, and correlate the bacterial patterns with how the tumors answer the drugs. If the patterns hold, the cup graduates from a nine-cent object to a clinical instrument, and the earliest conversation a cancer will ever have with a doctor will be conducted by the mouth, unprompted, as it has always been.
The cup holds about two milliliters. It has held that much, with steadily increasing confidence, for half a million years.