Individual chronic diseases are "an overlooked risk factor for cancer" that collectively contribute to an increased cancer risk similar to that seen with all major lifestyle risk factors combined, say researchers.

A prospective cohort study of more than 400,000 men and women shows that five common chronic diseases and their markers contributed to one fifth of new cancer cases (20.5%) and more than one third of all cancer deaths (38.9%).

Over an average follow-up of 8.7 years, the impact on cancer incidence and mortality of diabetes; pulmonary disease; and markers for cardiovascular disease, chronic kidney disease, and gouty arthritis shortened lifespan by 13.3 years in men and 15.9 years in women, the authors report.

Increased chronic disease risk scores were associated with increased risk for liver, bladder, kidney, stomach, oral, and colorectal cancer, the study showed. This suggests that "chronic diseases or underlying biological alterations may play an important role in the cause of these specific cancers," the study authors concluded.

The study was published online January 31 in the British Medical Journal.

These findings "revealed a previously overlooked yet substantial impact of chronic diseases on cancer risk" that is "just as important as five major lifestyle factors," say the researchers, led by Xifeng Wu, MD, PhD, from the University of Texas MD Anderson Cancer Center in Houston, Texas.

"Current cancer prevention strategies focus on lifestyle risk factors and do not consider chronic diseases as modifiable cancer risk factors," Dr Wu told Medscape Medical News. On the basis of the results of the current study, "a major contributor of cancer incidence and mortality will be missed if future cancer prevention strategies do not target chronic diseases," she said.

Recognizing that chronic diseases substantially increase cancer risk and shorten lifespan could stimulate better management of chronic diseases, improve overall health, and reduce cancer burden, Dr Wu suggested.

An additional finding from the study was that physical activity was associated with a nearly 40% reduction in the excess risks for incident cancer and cancer death associated with chronic diseases and markers.

"Clinicians may also want to recommend physical activity as an effective, inexpensive, and safe preventive strategy to reduce the risks of cancer and other chronic diseases," Dr Wu added.

Study Details

The observational study was carried out in Taiwan between 1996 and 2007. It examined data from 405,878 people without a history of cancer who underwent standardized medical screening.

The investigators evaluated the impact of five common chronic diseases accounting for most of the disease burden worldwide: cardiovascular disease (markers for which include blood pressure, total cholesterol, and heart rate), diabetes, chronic kidney disease (markers for which include proteinuria and glomerular filtration rate), pulmonary disease, and gouty arthritis (for which uric acid is a marker).

So, overall the team looked at eight chronic diseases and markers.

With the exception of blood pressure and pulmonary disease, six measures were individually associated with a statistically significant increased risk for incident cancer (adjusted hazard ratio [HR], 1.07 - 1.44).

Similarly, there was a statistically significant association between risk for cancer death and all eight diseases and markers (adjusted HR, 1.12 - 1.70).

The incidence of cancer associated with chronic diseases was 20.5%.

This compares with 24.8% for all five major lifestyle risk factors combined. These included smoking, insufficient physical activity (<3.75 metabolic equivalent hours per week), insufficient fruit and vegetable intake (fewer than two fruits and vegetables per day), overconsumption of alcohol, and obesity.

The incidence of cancer mortality associated with chronic diseases was 38.9%, compared with 39.7% with lifestyle risk factors combined.

Smoking, the most carcinogenic lifestyle risk factor, resulted in the most life-years lost in both men and women: 4.3 and 4.8 years, respectively.

Although previous studies have shown that certain chronic diseases share common risk factors and may predispose to cancer, these earlier investigations have focused primarily on the impact of individual diseases and disease markers rather than on chronic diseases as a group, the study authors point out.

To date, three studies have estimated the contribution of diabetes to overall cancer or specific cancers, which ranged from 1.4% for overall cancer incidence to 7.3% for pancreatic cancer mortality, Dr Wu said. "However, the individual contribution of the other seven chronic diseases or markers, including cardiovascular disease, pulmonary disease, and chronic kidney disease, have not been systematically explored," she noted.

"We believe that exercise is a promising approach to reduce the cancer risk associated with chronic diseases and markers since our results showed that physical activity is associated with a nearly 40% reduction in the cancer risk associated with chronic diseases or markers," said Dr Wu. "In addition to physical activity, avoiding smoking and alcohol consumption, maintaining healthy weight, and healthy diet are also important in cancer prevention strategies."

This study was funded by the Center for Transnational and Public Health Genomics at MD Anderson Cancer Center and by the Taiwan Ministry of Health and Welfare Clinical Trial Center. Dr Wu and study coauthors have disclosed no relevant financial relationships.

BMJ. Published online January 31, 2018. Full text

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