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Using computational techniques to analyze the data, the researchers calculated measures of diversity inside the tumors. Essentially, they counted cell varieties and measured the genetic difference, or divergence, between those varieties. "Simply put, we took ecology measures of species diversity and translated them into measures of cell diversity within tumors," Maley says. The found a striking correlation between increased diversity of tumor cells and progression to cancer. For every additional cell variety detected in a tumor, the patient was twice as likely to progress to cancer.

Maley suggests that genetically diverse tumors have a high probability of generating mutant cells that will flourish and spread, allowing the tumor to transform and grow. In the future, in addition to serving as a biomarker for cancer risk, he adds, measures of genetic diversity might help doctors assess the success of cancer prevention therapies.

In fact, he speculates, genetic diversity among tumor cells might help explain why therapy sometimes fails. If a tumor contains a diverse population of cells, some of those cells are more likely to resist treatment, Maley says. Adapting to and surviving chemotherapy, these resistant cells could breed, leading to a cancer relapse. He hopes to pursue this hypothesis in the future. "More immediately," he adds, "we intend to validate the new study with other cohorts and other types of tumors."