Something Out There is Causing Cancer … but it’s probably not as mysterious as you think

December 22, 2015

A common scene plays out every day in doctors’ offices, hospitals and even on social media: Somebody has cancer, and we all speculate why. The more this happens and the closer it gets to home, the more we’re convinced that something out there—something in the environment—is the culprit.

In many cases we’re correct, says John Jalas, MD, PhD, assistant professor of pathology at the John Wayne Cancer Institute at Providence Saint John’s Health Center. “At least two-thirds of cancers are caused by environmental factors.”

Yet we don’t need Erin Brockovich to help us figure out what’s contributing to the overwhelming majority of these cases. Cigarette smoking, drinking too much alcohol, poor diet, physical inactivity and being overweight put us at increased risk for cancer.

“About one-third of all the cancer deaths in this country could be prevented by eliminating the use of tobacco,” says Dr. Jalas. After that, being overweight or obese appears to be the most important preventable cause of cancer.

Still, we all know people who do everything right and get cancer … or people who do everything wrong and remain cancer-free. What gives?

Jalas“The more we learn about cancer, the more we see it’s an extremely complex interplay of factors—including environmental exposure and genetics. In the end, there are still many cases where we can’t pinpoint why somebody got it and somebody else didn’t,” says Dr. Jalas.

As far as environmental exposures go, it simply isn’t possible to predict whether a specific exposure will cause a particular person to develop cancer. Yet Dr. Jalas says he believes labor regulations to prevent unnecessary risk to workers in certain industries, as well as measures such as California Prop 65 (the safe drinking water and toxic enforcement act of 1986), are necessary.

“Our environment impacts our health. We shouldn’t be scared to death about that, but we need regulations and a general awareness that we should reduce the risk of harm where we can.”

Most people are aware that asbestos exposure, solvents or fine particles such as those produced in furniture making, for example, increase cancer risk. Several other environmental exposures have been tied to cancer risk, including the following:


An estimated 20,000 lung cancer deaths in the United States each year–particularly among nonsmokers–are caused by ionizing radiation from radon exposure in homes. About one out of every 20 U.S. homes has elevated levels of this naturally occurring radioactive gas, which is odorless and invisible. How does it happen?

Radon is released during the natural decay of uranium, present in most rock, soil and water. That’s why higher levels can be found in certain types of rocky soil. Radon levels vary from home to home—even in the same neighborhood, but parts of Los Angeles, Ventura and Santa Barbara counties are known to be at increased risk for higher-than-average radon.

“The good news is that homeowners can easily test for radon and even take care of the problem relatively inexpensively,” says Dr. Jalas. Home radon testing kits are available at home improvement centers or for $7.95 through the California Department of Public Health Indoor Radon Program.

“We worry about our exposure to so many things we can’t control, and yet this one we can control and most people aren’t aware of it,” he adds.


Listen up, surfers and sunbathers: UV radiation from the sun changes your DNA. And not in a good way.

“When we look at genetic testing and sequencing of mutations that occur in cancer, there’s a characteristic change that occurs in the DNA due to UV radiation damage,” says Mark B. Faries, MD, director of the Donald L. Morton, MD, Melanoma Research Program at the Institute. “This is really a public health issue. We have to connect to the idea that skin cancer is caused by a carcinogen the same way tobacco causes cancer.”

The drive to get a tan is even similar in some ways to the drive to smoke, he adds. “Studies have actually found that among people who are frequent sunbathers, tanning causes the release of chemicals in the brain that mimic what drugs do for addicts.” Thus, they have a hard time breaking the tanning habit.


There’s no doubt about it: Certain viruses and bacteria increase the risk of several types of cancer. Human papillomavirus (HPV) increases the risk of cervical and anal cancer. Hepatitis B and C increase the risk of liver cancer. Epstein-Barr virus is linked to lymphoma. And Helicobacter pylori, the bacteria that causes peptic ulcers and chronic gastritis, has been linked to increased risk of stomach cancer.

Vaccines for children are available to prevent infection from HPV and hepatitis B; treatments are also available for hepatitis C and Helicobacter pylori.


A number of studies show an increased incidence of cancer (lung, skin and urinary cancers) in people exposed to PAHs, which are typically byproducts of petroleum processing and combustion. Foods that contain small amounts of PAHs include smoked, barbecued or charcoal-broiled foods, roasted coffees and sausages. PAHs are also in gasoline and diesel exhaust, soot, cigar and cigarette smoke.

“You have to use common sense with this one. You aren’t going to increase your risk much by eating BBQ occasionally or going to the gas station, but an increased risk gets more real for people who work around gasoline daily, for example,” says Dr. Jalas.


Of the nearly 900 active ingredients in registered pesticides in the United States, about 20 have currently been found to be carcinogenic in animals. In the United States the worst pesticides have been banned or their use restricted. Dr. Jalas says that’s enough protection for most of us.

“Studies have linked people with extremely high exposures to pesticides—occupations like farmers, pesticide applicators and crop duster pilots—to certain cancers. For most of us, though, the exposure we get from consuming trace amounts of pesticides is just not enough to cause concern, let alone cancer, although limiting our exposure makes sense.”

For that reason, Dr. Jalas washes his produce but doesn’t worry if it’s organic or not. However, Maggie DiNome, MD, acting director of the Margie Petersen Breast Center at Providence Saint John’s Health Center, says she errs on the side of caution. “Because I have such a strong family history of cancer, I try to incorporate many cancer-fighting, antioxidant-rich fruits and vegetables in my diet, and I try to keep it all organic just so I can minimize my exposure to pesticides and chemicals.”


A few drugs used to treat cancer (for example, cyclophosphamide, chlorambucil, melphalan) have been shown to increase the occurrence of other cancers, including leukemia. Immunosuppressants, such as cyclosporin and azathioprine for patients having organ transplants, have been linked with increased cancer risks, especially lymphoma.

And hormone therapies appear to elevate the risk of some cancers, though they often decrease the risk of others. For example: Long-term users of combination oral contraceptives (estrogen and progestin combination formulas) have substantially reduced risks of endometrial and ovarian cancers but an increased risk of early-onset breast cancer and liver cancer.

“There are always benefits and risks to any medication. The point is, if you take a medication, the benefits have to outweigh the risks. Always talk to your doctor about it,” says Dr. DiNome.


Despite occasional headlines to the contrary, there are some environmental exposures that, studies show, do not cause cancer.

Cell phones

Cells phones, and wireless phones to a lesser extent, emit radiofrequency energy—a form of nonionizing radiation. Ionizing radiation (such as that in radon) has been linked to increased cancer risk. A slew of studies, however, have not been able to link nonionizing radiation to increased cancer risk. Heating, which hasn’t been shown to be harmful, is the only clear biological effect. Bluetooth technology and our obsession with texting rather than talking, however, mean even warm ears are probably things of the past.


Living near an active volcano, surviving an atomic bomb or being exposed to iodine-131 fallout as a child puts people at increased risk of leukemia and cancers of the breast, thyroid, lung, stomach and other organs. But radiation from medical X-rays, including regular dental X-rays, don’t present enough exposure to come close to a real risk.

“Even if somebody got 10 chest CT scans, you still wouldn’t be at increased risk,” says Melanie Goldfarb, MD, assistant professor of surgery at the Institute. “Patients often question X-rays, but radiation exposure with needed X-rays is minute and in almost all cases technicians shield patients just for increased protection.”

According to Dr. Goldfarb, thyroid cancer is rising, but there’s nothing in the typical person’s environment that accounts for it. “The truth is, we don’t know enough about thyroid cancer yet. And so far, environmental factors don’t seem to be a cause.”

Genetically modified organisms (GMOs)

To label or not to label GMO foods is open for debate, and GMO opponents may have plenty of other charges. But Dr. Jalas says cancer shouldn’t be one of them. “Once you understand the process of genetically modifying foods, you can see that it is unlikely to contribute to cancer, however, more research is needed. Keep in mind that life-saving insulin for diabetes is produced by a genetically modified organism, which of course doesn’t promote cancer and actually saves many lives,” he says.