The direct-to-consumer genetic testing market has helped tens of millions of Americans not just learn about their family lineage, but also given them a microscopic view of their health.
Popular DIY tests – such as Ancestry DNA and 23&Me – offer a variety of kits depending on how much of a deep dive into your DNA you’re hoping to do, ranging from $99 to $200.
Kits that test your cheek swab for health markers may reveal genes that indicate an increased likelihood of breast, ovarian, and prostate cancers, helping customers – whether they have a family history of cancer or not – gain a better understanding of their individual risk.
But oncologists caution the at-home tests are not for everyone.
Direct-to-consumer tests are fairly limited in scope when it comes to variants they test for. 23&Me, for instance, only tests for 44 genetic variants in the BRCA1 and BRCA2 genes, which suggest a proneness to breast cancer, but there are more than 4,000 known variants that increase the risk.
23&me also tests for two variants in genes that increase one’s risk of colorectal cancer, though there are about 25 acquired gene mutations known to increase CRC risk.
Dr Mikkael Sekeres, an expert in blood cancers at the University of Miami, advised concerned customers to contact their doctors for a more comprehensive lab test instead of first trying an at-home test.
He added just a small proportion of cancers – between five and 10 percent – are believed to be associated with genetic variants, while the rest are caused by lifestyle and environmental factors like smoking and air pollution, calling into question whether these tests truly are the crystal ball that people want.
And doctors also warn that many people untrained in science may misinterpret their results or blow something out of proportion, leading to even more undue anxiety.
Popular DNA tests such as those made by ’23andMe’ can reveal certain gene mutations passed down from our parents that can point to cancer risk. But doctors fear these results could cause undue stress and anxiety. And many people won’t benefit
Dr Sekeres told the Washington Post doctors typically only order a specific test based on whether the information from those tests will actually lead to a meaningful difference in their care.
If they know the disease risk is low and that it may cause added cost and stress to the paint, they might skip it.
He said: ‘When it comes to at-home tests, I advise my patients to think like a doctor in this way.’
If the results are negative, the person will likely breathe a sigh of relief, and their stress will end there, even though that negative result does not mean they will never get cancer.
But if the test shows a positive result, how might that change their daily life, Dr Sekeres asked.
Will you tell your children of your genetic predisposition? Will you slash your alcohol intake and stop smoking to minimize your risk? Will you follow a strict clean-eating regimen and exercise for 30 minutes or more daily? Will you remember every single day before leaving the house to slather yourself in sunscreen?
Dr Sekeres said: ‘If the answer to these questions is “no,” you probably should not order the test.’
According to the National Cancer Institute, people who find they don’t carry a genetic variant that others in their family do can engender ‘survivor’s guilt,’ which can cause extreme shame and a false sense that a negative outcome could have been prevented.
And inconclusive results can cause uncertainty and stress.
There is also the risk of false-positive results, which can lead to stress and the financial cost of getting adequate follow-up testing ordered by a physician.
A 2018 report revealed a staggering 40 percent of raw data from direct-to-consumer genetic tests produced false positives.
And just because a test result might show a certain mutation, that does not mean the person is destined to develop cancer, though it does indicate an increased risk.
Anyone who sees a mutation on the BRCA1 gene, for instance, is likely to become extremely distressed. Having a BRCA mutation does not make cancer a foregone conclusion. Rather, having the mutation increases cancer risk by 45 to 85 percent.
At-home tests, which take into consideration a person’s ethnicity, have another major shortcoming: they only look for DNA changes passed down from parents. But, genes can undergo major changes throughout our lives.
About 90 percent of cancer mutations occur during a person’s lifetime due to factors like aging, environmental stressors, and random errors in cell division and growth, compared to around 10 percent of cancer genes passed down from our parents.
Dr Sekeres said: ‘It can take decades to acquire the mutations that cause cancer, and thus the reason most cancer is diagnosed in older adults, at a median age of 66 years in the United States.’
At-home genetic tests only detect gene mutations passed down from our parents, even though the vast majority of cancers are caused by mutations that occur throughout people’s lifetimes
Just three to five percent of colorectal cancer cases are linked to an inherited gene change. The remaining 95 to 97 percent, meanwhile, are caused by acquired mutations.
About five to 10 percent of breast cancer cases are thought to be hereditary, meaning that they result directly from gene changes. That means roughly 90 percent of cases are caused by acquired mutations.
But the BRCA1 and BRCA2 genes are perhaps the most well-known mutated genes that increase women’s susceptibility to breast cancer and ovarian cancer, as well as prostate cancer in men.
About 1 in 400 people in the general population carry one of these genes, but the rate is higher among those of Ashkenazi Jewish descent, with approximately 1 in 50 people affected.
The MLH1, MSH2, MSH6 and PMS2 gene mutations can lead to colorectal cancer, gastric, ovarian, and endometrial cancers and are colloquially known as Lynch syndrome. Almost one in 300 people have one of these mutations.
And TP53, which leads to a wide range of conditions including breast, bone, soft tissue, brain, adrenal gland, and blood cancers, is known is Li-Fraumeni syndrome. Around one in 5,000 people have inherited this variant.
Of those three, 23&me only tests for BRCA mutations.
Dr Sekeres said: ‘If you do test positive for a genetic mutation, the good news is that, while genetic mutations can place us at higher risk of developing cancer, there are interventions we can make to mitigate that risk.
‘Talk to your doctor about the best plan for you, which may include early screening and taking medications such as oral contraceptives or aspirin.’