This is a serious and age-old question. Kenneth Pienta, M.D., Donald S. Coffey Professor of Urology, Director of Research at the Brady, and colleagues are proposing a brand-new answer. They recently published their rationale for a new definition of cancer in Molecular Cancer Research.

The National Cancer Institute defines cancer as: “a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body,” and most definitions of cancer run along these lines.

But there’s a problem, Pienta says: “These definitions tend to describe what cancer looks like or does, but do not describe what cancer is or has become. Current definitions have not kept pace with the understanding that the cancer cell is itself transformed and evolving.”

Changing the mindset of what cancer is may change how we treat it.

The revised definition of cancer proposed by Pienta and colleagues is this: Cancer is a disease of uncontrolled proliferation by transformed cells subject to evolution by natural selection. “To the simplest definition of cancer, as a disease of uncontrolled proliferation of cells, our definition adds in the adjective ‘transformed’ — to capture the many tumorigenic processes that cancer cells adopt to metastasize. Adding “subject to evolution by natural selection” modernizes the definition “to include the genetic and epigenetic changes that accumulate within a population of cancer cells that lead to the lethal phenotype.”

Pienta and colleagues hope that by changing the mindset, “by understanding that cancer cells are actually following the principles of natural selection, we will help doctors, scientists, and patients better understand how cancer changes over time. This opens opportunities for developing optimal diagnostic and interventional strategies.”