LONDON (Reuters) - British researchers said on Tuesday they had identified a possible new mechanism that might explain how smoking can cause breast and bowel cancer as well as lung cancer.

The team, at the Christie Hospital, Manchester, said they had found that smokers have significantly higher levels of insulin-like growth factors in their blood than non-smokers. "We are excited about the findings of this research as they indicate a possible new mechanism to explain the development of some cancers," said research leader Dr. Andrew Renehan. "This has potential implications for cancer risk assessment and cancer prevention strategies in the future," he added in a statement. The findings were presented at the British Endocrine Societies' meeting in Harrogate, Yorkshire -- Europe's largest annual meeting of hormone specialists. Renehan said other research had recently established that insulin-like growth factors (IGFs) are linked to breast and colorectal cancer, prompting his team to examine associations between smoking and IGFs. The team looked at cigarette smoking histories in over 400 individuals, aged 55 to 65, attending a bowel cancer screening trial in Manchester. They found that long-term smoking significantly affected levels of IGFs and that this was related to length of cigarette use and number of cigarettes smoked. "The findings were dose-related and were statistically significant," he added in a telephone interview. "There was a 20 to 25 percent difference in IGF levels between the heaviest smokers and the non-smokers." Asked about the likely biological mechanism, he said it was known that growth factors could encourage cancer cell growth and protect abnormal cells against natural death. However he said that a much larger study would be needed to prove that smoking, levels of IGF, and cancer risk were all linked.

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