Overdiagnosis of thyroid cancer is inevitable when many cases, especially low-risk cancers, are identified during necessary investigations for benign thyroid conditions, Australian researchers say.
A Queensland study of more than 1,000 patients newly diagnosed with thyroid cancer between 2013 and 2016 found only 38% of patients had initially presented with symptoms such as a neck lump that was likely to be related to their diagnosis.
More patients were diagnosed in other contexts such as following imaging or surgery for benign thyroid disease, monitoring of autoimmune disease or a nodule, or unrelated imaging.
The study found that larger tumours and those with evidence of local spread were more likely to be diagnosed because of symptoms. Follicular cancers and cancers with BRAF mutations were more likely to be diagnosed on the basis of symptoms related to their larger size or high-risk features such as lymph node involvement.
“We also observed that almost a quarter of all participants had cancers, predominantly of the papillary type, that would be classified as lowest-risk,” the study authors said.
“The proportion of these potentially ‘over-diagnosed’ papillary microcarcinomas was higher amongst those diagnosed through surgery for benign thyroid disease or during imaging for other thyroid conditions (nodules or autoimmune disease).”
Dr Susan Jordan, head of the Cancer Causes and Care team at QIMR Berghofer Medical Research Institute, told the limbic that reducing the number of thyroid cancers diagnosed at surgery for benign thyroid disease was almost impossible.
“So people will have surgery to remove a goitre that is causing problems with swallowing or breathing and when the pathologist looks at the gland under the microscope they pick up some of these small cancers.”
“Having said that, once some of these small cancers are removed, they don’t require further treatment. But the cancer diagnosis is there and required by law to be sent to the cancer registry.”
“What we found in our study was that people were having a range of investigations for a range of different conditions, for example, CT scans of the head or neck, or an X-ray showing a thyroid mass and that leads to a cascade of testing that is often unavoidable.”
“People are getting so many tests that some of the overdiagnosis is unavoidable. But we did find that, even though the guidelines recommend that people don’t have fine needle aspiration (FNA) of small thyroid lesions, this was still happening in up to half of the cases.”
She said adherence to recommendations such as avoiding FNA on nodules less than 1cm and ultrasounds without a palpable abnormality would help to reduce some – but not all – of the over-diagnosis.
As a consequence, it was also important that affected people were not overtreated – perhaps by having less extensive surgery or less radioactive iodine therapy for small tumours.
“Ultimately, we need better diagnostic tools, potentially including molecular markers, to differentiate between indolent/lowest-risk cancers and those of greater clinical significance. Until such technology is available, it is likely that diagnosis of indolent thyroid cancers will continue to contribute significantly to the incidence of thyroid cancer,” the study authors concluded.