The relationship between chronic inflammation and cancer gets a careful look in a report in the journal Oncology (Vol 16, No 2: 217-229).

Some cancers are known to occur more frequently in people with certain inflammatory diseases — like inflammatory bowel disease and hepatitis.

The authors believe an understanding of what is going on in the cells of these diseases may one day lead to better prevention and treatment for cancer.

There is much evidence that chronic inflammation leads to an increased cancer risk. The types of chronic inflammation that lead to cancer are varied. They are caused by things such as viruses, asbestos exposure, or even the body's own digestive acids.

The longer the inflammation persists, the higher the risk of associated cancer.

"When people have a chronic inflammatory condition like inflammatory bowel disease, they have a five- to seven-fold higher incidence of colon cancer," said lead author Emily Shacter, PhD, senior investigator at the US Food and Drug Administration (FDA). "The hypothesis is that it is our bodies' own immune systems that are producing agents that cause cells in the colon to become cancer cells."

Acute (short-term) inflammation is a good thing, as our bodies send cells or agents to deal with an infection or a foreign body, such as a splinter, said Shacter.

But chronic inflammation often has certain factors and pathways that, "in the wrong place and at the wrong time," can encourage cancer growth, she said.

"It's not easy to cause a cell to become cancerous," Shacter said. "But if a certain sequence of events happens in such a way that a cell gets a growth advantage, it can go on to become a cancer cell. If we knew what was happening, we could possibly develop preventive strategies."

Even in inflammatory conditions, cancer is still relatively rare.

"In our body we have about a million mutations a day," said Michael Thun, MD, vice president of epidemiology and surveillance research at the American Cancer Society (ACS). "Most of them either get repaired or the cell commits suicide. It is only when a cell divides before it either repairs the DNA or commits suicide that the mutation becomes permanent."

"Whether or not inflammation is providing the earliest mutations in cancer isn't clear," he said. "But what is clear is that it provides the conditions in which an abnormal cell and its progeny (offspring) can replicate and survive and accumulate more mutations to become an invasive cancer."

Even so, Thun said, cancer "remains an uncommon event. Even in inflammatory conditions."

Thun said what helps control inflammation may point scientists in the direction they need to go to either prevent cancer or stop its progression.

"One example has been the interest in NSAIDs with colon cancer," he said. NSAIDs are non-steroidal anti-inflammatory drugs, such as aspirin or ibuprofen.

Shacter said another possible example now being explored is the role of oxidants — damaging substances produced by immune system cells — in inflammation and cancer.

While there's not enough evidence to recommend them yet, "we may eventually start giving kids antioxidant compounds so that some tumor isn't going to come up 20 years later," Shacter said. "Or hopefully do something even more targeted than that. The more we understand about the basic science, the more we can design interventions and treatments."