The DNA detectives who are hunting the causes of cancer

The endoscopy unit at Moi Teaching and Referral Hospital in Eldoret, Kenya. US surgeons are teaching local doctors how to carry out endoscopies and insert stents.

Story highlights

  • Scientists are looking inside the DNA of cancer cells to look for signatures of cancer-causing agents
  • Finding out what is increasing the risk of cancer can make lasting life-saving changes in public health

(CNN)Halfway up a hill overlooking the Great Rift Valley in western Kenya are two graves. One of them is a few years old now, bristling with bushy shrubs stretching bright green leaves towards a cloudless sky. The other is a freshly dug bed of rough red dirt planted with a white wooden cross. They are the final resting places of Emily's mother and father, who died within four years of each other.

Still a young woman, Emily now looks after her family's rural homestead near Iten -- a town famed for churning out long-distance runners and playing host to Mo Farah's training camps. We reach it by driving through urban sprawl and out into the hills, passing a seemingly endless stream of impossibly fit athletes pounding the roadside paths.
    Emily is busy cooking lunch when we arrive. Her kitchen is a small straw-capped mud hut built in the traditional style, similar to the other buildings that make up the homestead, with smoke pouring out of the door from an open fire and chickens scratching in the dirt nearby. It seems idyllic, but there's a killer on the loose around here, and we've come to track it down.
      That killer is squamous cell oesophageal carcinoma -- one of the two main forms of oesophageal cancer, which starts from the cells lining the oesophagus. Cases started piling up more than 60 years ago in South Africa, when a doctor working in the Transkei territories noticed an unusually high number of people dying from the disease, which was almost unheard-of before the 1940s.
      The situation in Africa seems to be no better today. Worldwide, an average of 5.9 people per 100,000 will develop oesophageal cancer each year. In East Africa, that figure rises to 9.7 people per 100,000. In Kenya specifically it's 18 in 100,000, while in Malawi it's even higher -- 24 in 100,000 -- making oesophageal cancer one of the three most common cancers in these countries.
      But even after decades of investigation, we still don't really know what's causing these hotspots.
        Smoke pours from an open stove in a rural kitchen near Iten, western  Kenya.
        East Africa isn't the only place in the world where this is happening. The Golestan region of Iran has one of the highest rates anywhere on Earth, and there are pockets of the disease in places as diverse as Henan province in north-central China and southern Brazil, although it's relatively rare in neighbouring Colombia.
        Other parts of the world have their own cancer problems: there are strangely high rates of bowel cancer in Slovakia and Denmark, although they have low rates of liver cancer. People in the Czech Republic are more likely to be stricken by kidney or pancreatic cancer than the populations of neighbouring Austria and Poland.
        Do these differences lie in inherited genetic variations, or is it something to do with lifestyle? Is there an unknown carcinogen lurking in the environment? Or maybe it's a bit of all three? The wild differences in rates of cancer across the world is a mystery -- but a crack team of detectives is on the case.
        Leading this team is Mike Stratton, director of the Wellcome Sanger Institute near Cambridge, UK, one of the largest centres in the world for DNA sequencing and analysis. Together with Paul Brennan at the International Agency for Research on Cancer (IARC) in Lyon, France -- the World Health Organization's cancer research arm -- and other teams in the UK and USA, Stratton has assembled the most impressive detective force in cancer research: a project known as Mutographs of Cancer.
        By peering deep inside the DNA of cancer cells, Stratton and his team are hunting for the unique mutational signatures that different cancer-causing agents and processes have left behind.
        "I've been interested in the idea that you can detect evidence of the exposures that are causing cancer for 20 or 30 years," Stratton explains. "A mutational signature is simply the pattern of mutations that is left by a mutational process, and a mutational process can be anything from exposing a cell to ultraviolet light to tobacco smoke to endogenous processes."
        The Mutographs team are recru