Carcinogens are substances with the potential to cause cancer. The World Health Organization’s International Agency for Research on Cancer has rated more than 1,000 agents as carcinogenic to humans, probably carcinogenic to humans, possibly carcinogenic, not classified as to its carcinogenicity to humans and probably not carcinogenic to humans.

The term “probable human carcinogen” has been in the news recently with the voluntary recall by different companies of dozens of prescription drugs with the active pharmaceutical ingredient valsartan, losartan or irbesartan used to treat common cardiovascular conditions like high blood pressure.

The medications recalled were due to trace amounts in their active ingredient of either N-nitrosodimethylamine (NDMA) or N-nitrosodiethylamine (NDEA).

These are chemical compounds in the nitrosamines class and are considered to be probable human carcinogens by both IARC and the U.S. Environmental Protection Agency. The two are sometimes produced as an unintended byproduct of a manufacturing process.

Their detection in valsartan tablets was first announced by the Food and Drug Administration in July and the recall of products thought to have been contaminated as a result of the chemical process that makes their drug substance has continued.  

The FDA is conducting an ongoing investigation and has published interim acceptable intake levels of nitrosamine impurities for manufacturers to ensure that finished drug products are safe and not subject to recall.

According to the FDA, this acceptable intake is a daily exposure to a compound such as NDMA or NDEA that results in a 1:100,000 cancer risk after 70 years exposure, or less than one additional case of cancer for every 100,000 people.

It has been estimated that Americans use 100,000 chemicals and that 1,000 new chemicals are introduced each year.

The Frank R. Lautenberg Chemical Safety for the 21st Century Act amended the 1976 Toxic Substances Control Act to enhance, among other powers, the EPA’s ability to evaluate industrial chemicals manufactured or processed in the U.S. over the past 10 years.

Some chemicals, like asbestos and arsenic, are known to cause cancer in humans, others are known to be carcinogenic in animals and are considered probable carcinogens in humans as a result.

It is not easy for researchers to evaluate which chemicals may cause which cancers, as cancer can be the result of many factors and take a long time to develop.

Carcinogens can directly cause cancer by how they change a cell’s DNA or in conjunction with other chemicals or they can cause it by how they are metabolized by the body.

The International Agency for Research on Cancer has rated both tobacco smoking and the consumption of processed meat as known human carcinogens — the latter over concerns that the curing process for such mean can cause potentially cancer-causing compounds.

It is estimated that at least 250 of the 7,000 chemicals in tobacco smoke are harmful and that 69 of the 250 can cause cancer.  Mortality rates among smokers are said to be three times higher than among people who have never smoked.

Second-hand smoke is classified as a known human carcinogen as well and is said to be responsible for some 7,500 lung cancer deaths among adult non-smokers each year in the United States.

Cancer-risk concerns have been raised over the vaped aerosol of e-cigarettes as well as the chemicals used in their flavorings.

An individual’s risk for developing cancer from a carcinogen depends on a number of factors including how much they were exposed and over how long a period of time.

Lifestyle recommendations for cancer prevention remain good advice for any of us to follow.

These include engaging in daily physical exercise, wearing sunscreen against the sun’s ultraviolet rays, maintaining a healthy weight, eating a diet with a variety of vegetables, fruits and grains, keeping up with recommended screenings and being aware of what is in the products that we use and consume.

Dr. Wilson Mertens is Vice President and Medical  Director, Cancer Services at Baystate Health’s Baystate Regional Cancer Program.