Ankylosing spondylitis (AS) is widely known to cause certain symptoms and complications in areas of the body other than the spine — such as inflammation in the eyes (uveitis) and the aorta, the largest artery in your body (aortitis).
Another area of research in recent years has been the connection between AS and cancer risk. Decades ago, ankylosing spondylitis was often treated with radiation to reduce spinal inflammation — a treatment that raised the risk of leukemia and other cancers.
Since then, drugs have replaced radiation as the main treatment for AS, and rates of cancer in people with AS have dropped. But many researchers still wonder if the disease itself, or certain drug treatments, may increase the risk of certain cancers.
So far, the results are reassuring in the sense that no dramatically increased cancer risk has been demonstrated. But there’s some evidence that having AS may somewhat increase your risk for certain kinds of cancer.
Here’s an overview of the latest evidence on AS and cancer risk, and how rheumatologists put this information into context with their patients.
Mixed Results in Studies
In studies examining the link between AS and cancer, the results have been different for different study populations.
In one analysis of two Scandinavian populations between 2001 and 2011, reported in a review published in March 2018 in the journal Frontiers in Medicine, researchers found an increased cancer risk of only 10 percent in people with AS and related diseases — too small a difference to conclude that it wasn’t due to chance or other factors.
In a study of the Taiwanese national health insurance database, published in August 2017 in the journal Oncology Letters, people diagnosed with AS between 2000 and 2008 were found to have an overall cancer risk 15 percent higher than similar people without AS. In particular, the risk of blood cancers in both sexes, colon cancer in women, and bone and prostate cancer in men was higher. The gap in cancer risk was greatest in people under age 35, with people with AS about twice as likely as others to develop cancer.
And in a study of U.S. Medicare databases between 1999 and 2013, presented at the American College of Rheumatology 2018 annual meeting, higher rates of certain cancers — but lower rates of others — were seen in people with AS older than 65. Rates were 57 percent higher for kidney cancer, 49 percent higher for melanoma, 43 percent higher for thyroid cancer, and 44 percent higher for leukemia. But they were also 42 percent lower for esophageal cancer, 45 percent lower for stomach cancer, and 28 percent lower for lung cancer.
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What to Make of the Evidence?
It’s hard to know exactly what to make of these conflicting results. But one solid conclusion can be drawn from all the studies: “There isn’t a huge increase in risk” for cancer, says Eric Ruderman, MD, a rheumatologist and a professor of medicine at Northwestern University Feinberg School of Medicine in Chicago.
Dr. Ruderman notes that since people with AS are more likely to have frequent medical visits, studies that find an increased risk of cancer may have an “ascertainment bias.”
“You have to consider that maybe you’re just picking stuff up better, because you’re taking good care of people and doing a lot of screening,” Ruderman explains. “Unless you understand what the mechanism would be, I’m always a little cautious about assuming” that an increased cancer risk is real.
A Plausible Mechanism for Higher Risk
But there is a plausible mechanism to explain certain cancers in people with AS, especially leukemia and lymphoma, according to both Ruderman and Weiwei Chi, MD, a rheumatologist and an assistant professor of medicine at the Icahn School of Medicine at Mount Sinai in New York City.
“Theoretically, it makes sense that there’s an increased cancer risk in patients with AS,” says Dr. Chi, who notes that a higher risk for immune-cell cancers in people with rheumatoid arthritis (RA) is well documented.
“It’s thought to be driven by your constantly active immune system and inflammation, which leads to production of more immune cells” and an increased risk that some of these cells will become cancerous, she explains. “AS and RA share a lot of features in common, in terms of overactive immune cells and chronic inflammation.”
But Actual Evidence Lacking
But a theoretical link and actual evidence are two different things. And on the basis of the data available, the cancer risk associated with AS is low — compared with both related conditions like RA, and the risk of other AS complications.
Another theoretically plausible increased risk of cancer — from the drug class TNF inhibitors, which is a common AS treatment — also largely hasn’t been supported by data, according to Chi. “The patients aren’t at increased risk for any particular cancers compared with other people who have the same medical condition who aren’t taking this medication,” she says.
Because cancer risk in people with AS is so low in the first place, it’s hard to know whether effectively treating AS brings it down even further. “To my knowledge, there’s no such data yet in AS,” unlike in RA, says Ruderman.
No Demonstrated Need for Extra Cancer Screenings
There’s also no evidence to support extra screening for cancer in people with AS, although it’s still a good idea for doctors to ask about any problematic symptoms, says Chi. “I usually ask them about fever, weight loss, night sweats — things that could point toward an underlying cancer.”
If you have any problematic symptoms, Chi says, certain blood tests or imaging may be in order. But this is the case regardless of whether you have AS.
So get recommended cancer screenings based on your age and sex, and report any troublesome symptoms to your doctor. Beyond that, when it comes to cancer, there’s not a whole lot for people with AS to worry about.