Boston, MA - The smokeless tobacco product snus, which is used mainly in Sweden but also is sold in the U.S., may increase the risk that men with prostate cancer will die from their disease, and the risk that they'll die prematurely from any cause, according to a new study led by researchers at Harvard T.H. Chan School of Public Health. The findings, which build on previous studies showing increased risk of death from prostate cancer in smokers with the disease, suggest that nicotine or other non-combustion-related components of tobacco may play a role in prostate cancer progression.

The study will appear in the October 12, 2016 issue of the International Journal of Cancer.

"Snus has been suggested as a less harmful alternative to smoking because it lacks the combustion products of smoking that are associated with cancer risk. However, we found that men with prostate cancer who used snus were at increased risk of premature death," said co-first author Kathryn Wilson, a research scientist in the Department of Epidemiology at Harvard Chan School.

Snus is a powdered tobacco product, often sold in teabag-like sachets, that is placed under the upper lip for extended periods. It contains nicotine but no combustion components, and has not been previously studied in relation to prostate cancer survival.

The researchers analyzed health data collected from Swedish construction workers during preventive health check-ups between 1971 and 1992, including a tobacco use questionnaire completed during each man's initial check-up. Of these men, 9,582 later developed prostate cancer. About half of the subjects died during the follow-up period--2,489 from prostate cancer.

Compared with those who never used tobacco, those who used snus but did not smoke had a 24% increased risk of dying from prostate cancer and a 19% increased risk of dying during the study period from any cause. Among men whose cancer had not spread, increased risk of death from prostate cancer for exclusive snus users was three times higher than for never-users of tobacco.

"There is some evidence from animal studies that nicotine can promote cancer progression, and snus users have high blood levels of nicotine. Snus users are also exposed to other carcinogens in tobacco even though it is a smokeless product," said Sarah Markt, research associate in the Department of Epidemiology. "Taken together, this suggests that the health effects of smokeless tobacco products should be carefully studied by public health officials."

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Other Harvard Chan authors involved in the study included Jennifer Rider and senior author Lorelei Mucci, associate professor of epidemiology.

Wilson, Rider, and Mucci were supported by Prostate Cancer Foundation Young Investigator Awards. Markt was supported by a T32 training award from the National Cancer Institute (NIH T32 CA09001).

"Snus use, smoking and survival among prostate cancer patients," Kathryn M. Wilson, Sarah C. Markt, Fang Fang, Caroline Nordenvall, Jennifer R. Rider, Weimin Ye, Hans-Olov Adami, Pär Stattin, Olof Nyrén, Lorelei A. Mucci, International Journal of Cancer, October 12, 2016, doi: 10.1002/ijc.30411

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