There has been a dramatic increase in the incidence of the thyroid cancer, largely driven by the increased diagnosis of papillary cancers (PTC).
The department of otolaryngology at the Royal College of Surgeons in Beaumont Hospital have, in conjunction with the National Cancer Registry, completed a national thyroid cancer audit between 1998-2012 where PTC was identified as the dominant subtype representing 49 per cent of thyroid cancer in 1998, increasing to 86 per cent in 2012.
In the 2010-2012 time period, Irish people were 3.7 times more likely to be diagnosed with PTC than 1994-1996. This increase in PTC has also been reported internationally.
According to International Agency for Research on Cancer, the rate of thyroid cancer detection has more than doubled in France, Italy, Croatia, the Czech Republic, Israel, China, Australia, Canada, and the United States. In South Korea in 2011, the rate of thyroid- cancer diagnoses was 15 times that observed in 1993.
In the US, it is estimated that 87 per cent of the papillary cancers now detected are under 2cm in size. Furthermore, 49 per cent are under 1cm in size.
These are largely non-palpable, but can be defined and diagnosed by non-clinical means such as ultrasonography.
At least one third of adults harbour small papillary thyroid cancers, the vast majority of which will not produce symptoms during a person’s lifetime. This is called the “subclinical reservoir”.
What we are witnessing around the world is increased exposure to this subclinical reservoir. It is well documented that 50 per cent of people aged 50 have thyroid nodules. We used to focus on the size of these nodules but now we’re more interested in the ultrasonographic characteristics of the nodule independent of its dimensions.
In an effort to tailor the treatment according to the severity of the cancer we now consider prognostic factors and perform a “risk” stratification assessment on each new cancer patient.
There are many risk stratification models. The best known, being “GAMES” criteria from the Memorial Sloan Kettering Cancer Centre in New York.
This stands for grade – appearance of the tumour; age of the patient – greater or less than 45 years old; metastases extra thyroidal extension (where tumour is found to burst through the gland; and size of the tumour). Using this model we can now estimate the risk status of a patient to be low, intermediate or high.
Thankfully the vast majority of patients fall under the low-risk thyroid cancer category.
In Ireland, results from our recent audit with the NCR, confers a 5, 10 and 15-year survival of 98.7 per cent, 98.2 per cent and 98.2 per cent respectively. These results correlate with international statistics.
It’s not all good news however. Despite this recent surge in disease incidence, thyroid cancer mortality over the last 40 years has remained relatively constant.
The incidence of all aggressive variants, such as poorly differentiated or undifferentiated (anaplastic) subtypes, remains unchanged. These are the tumours which continue to account for the majority of thyroid cancer mortality. Our failure to cure these diseases is the real controversy in thyroid oncology.
The history of thyroid surgery dates back to 952 AD, when Albucasis performed the first total thyroidectomy using opium sedation. After this, at one point, surgeons refused to perform thyroid surgery because of the potential complications.
In surgery today there are a number of common misconceptions of thyroid cancer therapy including the fact that all patients need all of their gland removed, an operation called a “total” thyroidectomy and that all patients need radioactive iodine ablation (RAI). This was the recommendations as best practice in the past, but contemporary medical evidence now reflects that low-risk thyroid disease does not require a total thyroidectomy and does not require RAI.
These conclusions have been reached after numerous reports in the literature comparing thyroid lobectomy versus total thyroidectomy and the use of adjunctive therapy such as RAI. A recent 2015 report from the SEER (Surveillance, Epidemiology and End Results) database in the US and the NCDB (National Cancer Data Base) reviewed 43,032 patients.
After adjusting for patient and clinical characteristics, total thyroidectomy compared with thyroid lobectomy was not associated with improved survival for patients under 45 years of age with cancers 1.1cm to 4cm in size. A report in 2014 of 61,775 patients found similar results.
A thyroid lobectomy is however not always appropriate. If patients are found to have aggressive features this puts them into an intermediate or high-risk category and does warrant total removal with possible additional treatment. The real challenge going forward in thyroid oncology is to identify the small group of patients who have high risk aggressive cancers and offer more effective treatment.
