Cancer is caused by damaged DNA — which produces mutant cells that multiply and destroy healthy ones. Now, researchers have found that smoking-related cancer can be detected early in cheek swabs that pick up damaged DNA, according to a study published in JAMA Oncology.

The study involved a research team from the University College London, who examined epigenetic changes in the DNA, which show which genes have been turned on or off due to damage and cancer. These epigenetic changes can be caused by toxic environmental exposure to cigarette smoke or pollution, so the researchers wanted to find out if taking cheek swabs could identify potential damaged DNA caused by smoking. The cheeks are directly exposed to cigarette smoke, which would make them a solid place to collect cells.

The researchers took buccal cells from 790 women born in 1946; they also had information about the participants’ smoking history. They found that buccal cells from smokers showed changes to their epigenomes, as well as a 40-fold increase in abnormal methylation sites. They concluded that smoking indeed caused big epigenetic changes.

With this in mind, they then examined 5,000 different tissue samples — normal, pre-cancerous, and cancer tissues from 15 different epithelial cancer types — in order to see if these epigenetic changes forecasted cancerous tissue. It turns out that this epigenetic “program” was able to tell the difference between normal and cancerous tissue with nearly 100 percent sensitivity and 100 percent specificity, no matter what organ the cancerous tissue originated in.

“These are significant results for our core interest which is decoding women’s cancers,” Professor Martin Widschwendter, one of the study’s authors, said in the press release. “We are a big step closer now to unravelling how environmental factors cause cancer. These results pave the way for other studies in which easily accessible cells can be used as proxies to highlight epigenetic changes that may indicate a risk of developing cancer at a site where cells are inaccessible.”

In other words, the researchers hope that their results can help identify oft-hidden cancers, like ovary, breast, or endometrial cancer, earlier on. In addition, “the results… demonstrate that smoking-related DNA damage to the epigenome of certain genes had been reversed in ex-smokers who had quit 10 years previously before sample collection, highlighting the key health benefits of quitting smoking, or not taking it up at all,” Widschwendter added.

Today, early detection in cancer is becoming more and more important. Along with cheek swabs, researchers have been working on developing — and making mainstream — a type of early detection test that identifies damaged DNA in the blood, referred to as a liquid biopsy. These early detection tests hold promise for identifying cancer sooner and thus treating it faster.

“This research gets us closer to understanding the very first steps in carcinogenesis and in future may provide us with much-needed tests for risk prediction and early detection,” Andrew Teschendorff of the UCL Cancer Institute, lead author of the study, said in the press release.

Source: Teschendorff A, Yang Z, Wong A, Pipinikas C, Jiao Y, Jones A. Correlation of Smoking-Associated DNA Methylation Changes in Buccal Cells With DNA Methylation Changes in Epithelial Cancer. JAMA Oncology. 2015.