Study Estimates That 22% Of Breast Cancers Are Overdiagnosed And Won’t Ever Cause Harm
A study out of Australia has found that early detection of harmless cancer cells has led to significant overdiagnosis. This, in turn, has led to unnecessary surgery and risks. Breast cancer and prostate cancer were estimated to be the most overdiagnosed cancers.
Not all cancer cells are created equal and can carry different risks. People can go years or even their whole lives without knowing they have a tumor growing in their body, because it’s never going to cause them harm and doesn’t cause symptoms. Overdiagnosed cancers are those not destined to cause symptoms or death.
Researchers found that improved screening methods are one reason why there has been an increase in cancer diagnosis over the last 40 years or so — even as cancer deaths have either fallen or stayed the same. They determined the risk of overdiagnosing five different cancers: breast, prostate, renal, and thyroid cancers, and melanoma.
The study was published in the Medical Journal of Australia and led by researchers from Bond University in Queensland.
Researchers took data in Australia from 1982 and compared it to data from 2012. They found that Australian patients were much more likely to be diagnosed with cancer in 2012 — even though the risk of cancer death was not the rise.
That means that up to 11,000 cancers in women and 18,000 cancers in men were detected in 2012 that may not have even needed diagnosis, let alone treatment.
They found that 24% of all cancer diagnoses in men (including 16% of invasive cancer diagnoses) were overdiagnosed. They estimated that 42% of prostate cancers, 42% of renal cancers, 73% of thyroid cancers, and 58% of melanomas (with invasive melanomas coming in at 22%) were overdiagnosed.
For women, they found that 18% of all cancer diagnoses (including 8% of invasive cancer diagnoses) were overdiagnosed. They also estimated that 22% of breast cancers (with invasive breast cancers coming in at 13%), 58% of renal cancers, 73% of thyroid cancers, and 54% of melanomas (with invasive melanomas coming in at 15%) were overdiagnosed.
“Cancer treatments such as surgery, radiotherapy, endocrine therapy, and chemotherapy can cause physical harm, but the risks are considered acceptable if diagnosis is appropriate,” the authors said. “When someone is unnecessarily diagnosed with cancer, however, they can only be harmed by treatment, not helped.”
Prostate and breast cancers are the most overdiagnosed, and this makes sense, as our methods for detecting these cancers have improved in the last several decades. After mammograms began in the ’80s, there was a 50% increase in breast cancer diagnoses in the U.S. When screening for prostate cancer began a few years later, the number of diagnoses for that doubled, too.
“The problem is that some screening identifies abnormal cells that look like cancer but don’t behave like cancer,” said physician Paul Glasziou from Bond University.
This research isn’t unique to Australia, either. Research in Denmark found that mammograms often detected small tumors that may not ever pose a risk, and mammograms also didn’t lower the rate of detection for late stage tumors. Research in the UK found that for every one life saved through breast cancer screening, roughly three women will be overdiagnosed with breast cancer that would never have posed a risk. A recent study in the U.S. found that rates of thyroid cancer, kidney cancer, and melanoma are climbing, while cancer deaths have stayed the same.
“Many people have assumed that additional screening is the best thing for population health, but in fact it may not be. You don’t test a population to health,” said Gilbert Welch from Brigham Women’s Hospital.
There’s not clear-cut answer to this problem, and researchers agree that screening is crucial for the fight against cancer. We just need to find the sweet spot between too much and not enough cancer testing. More research is needed.