The thyroid cancer epidemic that fizzled

Recently, doctors have been baffled by what's being considered a disturbing increase in rates of thyroid cancer. They're up a lot -- nearly 150 per cent over all. The biggest increase is in women age 30 to 59. Last month, a controversial study published in the New England Journal of Medicine concluded that the situation may not be as dire as the numbers would suggest.  

We've seen a big increase in diagnosed cases of thyroid cancer mostly in western nations including Canada - an increase far greater than that seen with most other cancers.  When researchers see numbers go up like that, they ask: is it an absolute increase in the number of cases or are doctors just getting better at detecting it?  So, the researchers looked at cancer registry data from various countries to see how rates of thyroid cancer changed over time - and to see what, if any, risk factors (things such as radiation exposure, diet and environmental factors) might have contributed.  

As the researchers discovered, there were no such risk factors during the study period. The authors concluded that there was no big increase in rates of thyroid cancer at all. What they found was a big increase in the detection of a relatively benign form of cancer called papillary thyroid carcinoma (PTC).

But what made this particular form of thyroid cancer became more detectable?

Turns out the countries with the highest prevalence of thyroid cancer had two common factors. First, they had adopted screening programs for early detection of thyroid cancer. That means they didn't wait for patients to have symptoms such as a lump in the neck and difficulty swallowing, but went looking for cancers before they caused symptoms. The second factor behind the increase was better access to ultrasounds, CT scans, and MRI's that identified smaller and smaller cancers. The rise in detection tracks perfectly with the increased availability of ultrasound pictures.  

The trouble with early detection is that you can't tell by looking at the picture if the cancer is malignant or benign. Since most cancers turned out to be benign, the authors of the study concluded that a whopping 70 to 80 per cent of all cases of thyroid cancer detected by doctors are harmless. To even call them cancers may be the latest example of what the researchers call "overdiagnosis."

Overdiagnosis comes from book entitled Overdiagnosed:  Making People Sick in the Pursuit of Health by Gilbert Welch, Lisa Schwartz and Steven Woloshin - three American doctors.  It refers to the diagnosis of a so-called disease that will never cause symptoms or death during a patient's lifetime. Not surprisingly, many of the examples of overdiagnosis involve cancer.  Prostate cancer is a prime example. Although some men have highly malignant prostate cancer, many do not, and are destined to die with, but not of, prostate cancer.  Other examples include borderline high blood pressure, gastroesophageal reflux disease, osteoarthritis and obesity.

The problem with overdiagnosis is that it leads to overtesting and overtreatment.  Suppose your doctor does a 'routine' ultrasound of your neck that detects a small growth on your thyroid. Chances are, if not detected, it won't kill you and won't ever bother you.  But now, your doctor is obliged to send you for a biopsy.  And when the diagnosis comes back as papillary thyroid cancer or PTC, you have surgery to remove the cancer and part of your normal thyroid.  You get side effects from the drugs, the biopsies, the diagnostic tests plus surgery plus needless anxiety - all for a cancer that won't kill you and won't even harm you.  

An observational study in Japan showed that the outcome of patients with PTC was the same whether managed by removing it surgically or careful surveillance.  Another problem with the PTC epidemic is the rising cost of care; close to $2 billion a year  in the United States alone.

Now that doctors are becoming aware of overdiagnosis, changes are coming.  Last year, the American Thyroid Society recommended watching lumps less than one centimetre in diameter instead of cutting them out.  And experts have recommended taking the word cancer out of the diagnosis of these non-lethal lumps and have renamed them as 'noninvasive neoplasms.' Nice try, but to me, the word neoplasm sounds just as serious.

Name aside, it takes time for new guidelines to make their way to the front lines.  So, in the meantime, if you get some bad news about a possible thyroid cancer, ask the doctor if he or she has found a thyroid lump that won't harm you -- and is therefore making an 'overdiagnosis."  

The answer just might save you a whole lot of unnecessary treatment as well as anxiety.