How much thyroid gland is enough? Can you get by with half of one?

That question is relevant to the more than 50,000 Americans diagnosed with thyroid cancer each year. As we point out in a study published Wednesday in the New England Journal of Medicine, it is also a question that doctors who treat thyroid cancer need to give more attention to, while the rest of us consider the broader questions about the appropriate intensity of treatment for early cancer.

First, some background on thyroid cancer. Although it is a rare cause of death, autopsies often show the existence of what is called papillary thyroid cancer. In other words, this is typically a cancer you die with — not from.

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Before the mid-1990s, the incidence of thyroid cancer had been relatively stable in the United States, at about 5 cases per 100,000 Americans. But since then, the incidence has tripled as ultrasound, MRI, and CT scans now detect small papillary thyroid cancers that cannot be felt. Yet despite this dramatic increase in new cases, the death rate from thyroid cancer has been rock stable.

It’s a clear-cut case of cancer overdiagnosis: the detection of cancer not destined to cause symptoms or death. To be sure, doctors never know for sure who is overdiagnosed. We have some clues, and in thyroid cancer those clues are the size of the tumor (small) and the cell type (papillary). Some people with these cancers are now being offered active surveillance. That means carefully watching the cancer over time and intervening only if it gets bigger or spreads. But others, having heard the word “cancer,” want treatment right away.

This is where the whole/half thyroid question comes in. Total thyroidectomy, the removal of both lobes of the thyroid, has been traditionally viewed as the “complete” procedure for thyroid cancer, and some doctors add radioactive iodine therapy afterward to destroy any thyroid cells that might have been left behind. An alternative is to remove the lobe of the thyroid that contains the cancer, a procedure known as lobectomy, and leave the other lobe in place. Radioactive iodine therapy isn’t an option after lobectomy.

Patients diagnosed with small papillary thyroid cancer do equally well with either total thyroidectomy or lobectomy: 98 percent of them will not die from thyroid cancer over the next 25 years. That suggests that the cancer doesn’t need treatment to begin with or it is successfully treated by either of the two approaches.

It sounds like choosing between total thyroidectomy and lobectomy is a close call. It isn’t. Although there’s no difference in terms of cancer death, there’s a substantial difference in quality of life. The thyroid is an important organ: it regulates metabolism. After lobectomy, thyroid function fully recovers in more than three-quarters of patients. That’s not possible after a total thyroidectomy, and patients who undergo it need life-long thyroid replacement therapy.

While life with a daily thyroid pill is tolerable, total thyroidectomy also produces long-term complications that lobectomy does not. Any thyroid operation risks damaging the nerves to the voice box and thus voice function. Total thyroidectomy endangers all of these nerves, while lobectomy endangers only half of them. The thyroid also shares blood vessels with the four parathyroid glands that regulate the amount of calcium in the blood. After total thyroidectomy, at least 5 percent of patients have no parathyroid function. They must take multiple vitamin and calcium supplements, and often have disabling symptoms. There is no chance of this complication after lobectomy.

So if you are ever facing thyroid cancer and are on the fence with the whole/half thyroid question, we suggest keeping half.

Here’s the weird thing. As more small, low-risk thyroid cancers are being found, the chance that an individual requires intensive intervention decreases. So it would be logical to de-intensify the intervention by doing more lobectomies and fewer total thyroidectomies. But that’s not what is happening in the United States. As we showed in the New England Journal article, data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program indicate that 80 percent of patients with small papillary thyroid cancers are having their entire thyroid glands removed, up from 60 percent three decades ago.

Thyroid cancer surgery rates
The New England Journal of Medicine ©2018

Since most patients are unaware of the choices and the risks for treating thyroid cancer, clinicians must be driving this decision. Why would they steer people to the riskier procedure? It could be about money. Although surgeons are paid about the same for both total thyroidectomy and lobectomy, omitting radioactive iodine treatment threatens revenue streams for some endocrinologists and nuclear medicine physicians.

It could also be about ignorance. Sixty percent of the total thyroidectomies in the U.S. are performed by surgeons who don’t do many each year (10 or fewer a year), and the occasional thyroid surgeon may be unaware of current guidelines supporting lobectomy. Or it could be about true belief: all involved may simply believe that the more intensive treatment must be the best way to deal with cancer.

This issue is particularly relevant to women, who are three times more likely to be diagnosed with thyroid cancer than men. Yet men and women are equally unlikely to die from thyroid cancer. The extra thyroid cancers diagnosed in women isn’t explained by tumor biology — autopsy studies find a similar number of papillary thyroid cancers in each sex. It’s better explained by medical sociology. Women have more contact with medical care and receive more diagnostic scrutiny, thus more cancer is found.

It is increasingly clear that a number of cancers are scrutiny-dependent: breast, prostate, thyroid, kidney, and even lung cancer. The more scrutiny, the more cancer found — and the more likely that what is found represents overdiagnosis.

Increased scrutiny is sometimes part of a purposeful effort to find cancer early (what doctors call screening) and sometimes a side effect of diagnostic tests done for other reasons that lead doctors to stumble onto unsuspected cancers (also known as incidental detection). Purposeful or incidental, earlier detection of cancer means that doctors are increasingly confronted with patients who have small, low-risk cancers — many of which will neither harm health or shorten life.

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Part of the solution, of course, is to look less hard for early cancer. With respect to thyroid cancer, that means raising the threshold to biopsy. Both the American Thyroid Association and the American College of Radiology now recommend that small thyroid nodules not be biopsied. Similarly, doctors are no longer as quick as they once were to biopsy the prostate or the kidney, instead recommending monitoring for mild elevations of PSA (prostate specific antigen) and small masses on the kidney.

The other part of the solution is to de-intensify treatment for early cancer. Aggressive interventions that make sense for patients with large, high-risk cancers do not make sense for those with small, low-risk cancers. But it’s hard for doctors to de-intensify care.

Urologists have led the way by investigating active surveillance for low-risk prostate cancer. It is now standard practice for men with low-grade prostate cancer. Active surveillance is also being offered to some patients with thyroid and kidney cancer, some with pancreatic endocrine tumors, and is under investigation for the earliest form of breast cancer.

De-intensifying care can make doctors and patients nervous, but it’s the right thing to do. Primary care practitioners should introduce patients to the idea that not all cancers threaten life, while cancer doctors must make sure that the treatments they recommend aren’t worse than the disease.

Gilbert Welch, M.D., is professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice and the author of “Less Medicine, More Health — 7 Assumptions that Drive Too Much Medical Care” (Beacon Press, 2015). Thyroid surgeon Gerard M. Doherty, M.D., is surgeon-in-chief at Brigham and Women’s Hospital and Dana-Farber Cancer Institute and professor of surgery at Harvard Medical School.

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