Hurthle cell thyroid cancer is a rare thyroid malignancy that accounts for roughly 3 to 4% of all thyroid cancers. It develops from a distinct type of thyroid cell packed with abnormal mitochondria, giving it biological behavior and treatment considerations that differ from more common thyroid cancers. As of 2022, the World Health Organization officially renamed it “oncocytic carcinoma of the thyroid,” though most patients and many doctors still use the older name.
What Makes Hurthle Cells Different
Normal thyroid cells produce hormones using small, efficient energy-producing structures called mitochondria. Hurthle cells are thyroid cells that have accumulated large numbers of dysfunctional mitochondria, which makes the cells visibly larger under a microscope. They also have oversized nuclei with prominent central features that pathologists can identify on tissue samples. The name “Hurthle cell” is actually a historical misnomer. Karl Hurthle originally described a completely different type of thyroid cell in dogs back in 1894, but the name stuck in clinical practice for over a century.
These cells aren’t always cancerous. Hurthle cells appear in several benign conditions, including Hashimoto’s thyroiditis (a common autoimmune thyroid disease) and multinodular goiter. They can also form benign growths called Hurthle cell adenomas. The cancerous version, Hurthle cell carcinoma, is distinguished by its ability to invade surrounding tissue or spread to other parts of the body.
Why It’s Hard to Diagnose Before Surgery
One of the most frustrating aspects of this cancer is that a standard needle biopsy often can’t tell whether a Hurthle cell growth is benign or malignant. The cells from a harmless adenoma look essentially identical to cancer cells when examined from a biopsy sample alone. The critical difference, invasion through the capsule surrounding the tumor or into blood vessels, can only be seen when a pathologist examines the entire removed tumor under a microscope.
This means many patients first learn they have cancer only after surgery that was initially performed to remove a suspicious nodule. If a lobe of the thyroid is removed and the pathology report comes back showing carcinoma, a second surgery to remove the remaining thyroid tissue is typically recommended.
Genetic Drivers of the Disease
Hurthle cell carcinoma has a genetic fingerprint that sets it apart from other thyroid cancers. Rather than the single-gene mutations commonly seen in papillary thyroid cancer, Hurthle cell tumors are driven by widespread loss of entire chromosomes and a high rate of mutations in mitochondrial DNA. Researchers have found that mutations disrupting a specific part of the cell’s energy production machinery (complex I in the mitochondria) may be what triggers the characteristic buildup of dysfunctional mitochondria in the first place.
Several gene mutations show up repeatedly in these tumors, including changes in genes that regulate cell growth and survival. One particularly important mutation involves the TERT promoter, which is more common in aggressive, widely invasive cases than in tumors caught early. The presence of TERT mutations has been linked to shorter survival, suggesting it may play a role in pushing a thyroid tumor toward more dangerous behavior.
How It’s Treated
Surgery is the primary treatment. For most patients, this means a total thyroidectomy, the complete removal of the thyroid gland. This approach is especially recommended when the tumor is larger than 4 cm, shows signs of invading surrounding tissue, or when there’s suspicion that lymph nodes are involved. Removing the entire gland reduces the risk of recurrence and makes long-term monitoring more reliable.
For smaller tumors confined to one side of the thyroid, removing just the affected lobe (lobectomy) may be an option. This sometimes happens as a first step when the diagnosis is uncertain. If the final pathology reveals cancer, surgeons generally advise going back to remove the other lobe as well, because Hurthle cell carcinoma can be aggressive and sometimes grows in more than one spot within the gland.
Radioactive iodine therapy, which works well for many other thyroid cancers, has a complicated relationship with Hurthle cell carcinoma. It has long been believed that these tumors don’t absorb radioactive iodine effectively. However, research has shown that about two-thirds of patients do have some measurable uptake, ranging from 0.1% to 12%. This means radioactive iodine scanning is still worth doing after surgery, and the treatment may benefit some patients even if it’s less reliable than it is for papillary or standard follicular thyroid cancer.
Long-Term Monitoring After Treatment
After thyroidectomy, doctors track a blood protein called thyroglobulin every 6 to 12 months. Since thyroglobulin is produced by thyroid tissue, its levels should be very low or undetectable once the gland has been removed. A rising level can signal that cancer has returned or that some thyroid tissue remains. About two-thirds of differentiated thyroid cancers, including Hurthle cell tumors, produce enough thyroglobulin to make this a useful tracking tool.
The test has real limitations, though. Some patients produce antibodies against thyroglobulin that interfere with the measurement, causing falsely low readings. Others may have tumors that simply don’t produce much thyroglobulin to begin with. For those patients, imaging with radioactive iodine scans or other methods becomes the primary way to check for recurrence. If a tumor transforms into a less differentiated form over time, thyroglobulin levels may stop rising even when disease is present, which is why imaging remains part of the follow-up plan.
Survival and Prognosis
The overall outlook for Hurthle cell thyroid cancer is favorable for most patients, though it has historically been considered somewhat more aggressive than standard papillary or follicular thyroid cancers. In a study of 239 patients followed over nearly two decades, the 5-year overall survival rate was 89.4%, the 10-year rate was 77.2%, and the 20-year rate was 61.9%. When looking specifically at deaths caused by the cancer itself rather than other causes, the numbers are more encouraging: 94.6% at 5 years and 92.5% at 10 years.
Perhaps most reassuring, 86% of patients in that study had no signs of recurrence a full decade after surgery. The patients who tend to fare less well are those diagnosed at an older age, with larger tumors, or with cancer that has already spread beyond the thyroid at the time of diagnosis. Widely invasive tumors, particularly those carrying TERT promoter mutations, carry a worse prognosis than minimally invasive ones caught early. This makes the distinction between early-stage and advanced disease one of the most important factors shaping a patient’s long-term outcome.