There are 4 main types of thyroid cancer, papillary (accounts for 75% of cases), follicular (15%), medullary (5%) and anapalstic (rare). Hürthle cell carcinoma is classified by the World Health Organization as a variant of follicular thyroid cancer, but others believe it is a distinctly separate disease. The disease accounts for only 3% of all thyroid cancers. Researchers believe that its behavior is similar to follicular cell carcinoma, though it does tend to be more aggressive. Given how rare this tumor is, there are a limited number of reported cases and have been no clinical trials to determine the best treatment.
Hürthle cell cancer has the highest incidence of metastases among thyroid cancers. . Hürthle cell cancer may metastasize to lymph nodes in the neck but follicular cancer does not; both hurthle cell and follicular cancers may spread by invasion into blood vessels, which may give rise to metastases outside of the neck. It has been estimated that 10-20% of patients with Hürthle cell have metastatic disease (spread to lymph nodes or other areas of the body) at the time of diagnosis. The likelihood of this can be predicted by the pathology at the time of surgery; Hürthle cell cancers that are small and show no sign of invasion into blood vessels or lymph nodes are very unlikely to spread. Survival rates vary greatly in the published studies, depending on the characteristics of the individual patient such as age, and the invasiveness of the tumor, so it is difficult to generalize a long term prognosis. These tumors are most common between 50 and 60 years of age, but have been reported from age 20 to 85 years old.
Unlike many cancers, Hürthle cell cannot be definitively diagnosed with a fine needle aspiration (biopsy). While the biopsy may be suggestive of a tumor that may or may not be cancer, called a Hürthle cell neoplasm, the large majority of these will be found to be benign (called a Hürthle cell adenoma). The only way to confirm the diagnosis of cancer is by identifying capsular or vascular invasion (that is, invasive growth that is seen with cancer). This can only be determined after the nodule is surgically removed and examined by a pathologist in the laboratory. This need for surgery to confirm the diagnosis may change as genetic testing of biopsy samples improves but that is still several years away.
Once there is a diagnosis of a Hürthle cell neoplasm, surgery to remove the affected thyroid lobe is typically the next step to clarify the diagnosis. Only 15-30% of patients will receive a diagnosis of carcinoma after surgery, with the remainder finding the nodule was benign.
The main treatment of Hürthle cell carcinoma is surgery, but there is some controversy as to how extensive a surgery is required, given that some tumors will behave aggressively, while others do not. The initial size of the nodule and the patient’s age and general health may help decided on the extent of the first surgery In some cases, the entire thyroid gland is removed (total thyroidectomy) once the diagnosis is confirmed, along with any enlarged lymph nodes. Detection of cancer in any lymph nodes may lead to a more extensive lymph node dissection. Some experts feel total thyroidectomy is the best procedure because it allows follow up tests to be more effective, as residual thyroid tissue can affect these.
Radioactive iodine is a useful nonsurgical treatment for many types of thyroid cancers, but Hürthle cell cancer is only treatable by radioactive iodine in about 15% of the cases. A dose of radioactive iodine may be given to destroy the remaining normal thyroid tissue after surgery. This helps to make the follow up testing for recurrence more sensitive and may also show if the tumor is able to be treated by radioactive iodine. In some cases of extensive disease patients may be treated with external beam radiation therapy.
People facing a diagnosis of Hürthle cell carcinoma require a multidisciplinary team of doctors, including an endocrinologist, head and neck surgeon or endocrine surgeon, nuclear medicine physician, pathologist and, in a few cases, a radiation oncologist. Finding an experienced team is important in treating this rare cancer. After surgery, patients will require thyroid hormone supplementation and monitoring for life. Monitoring for tumor recurrence is done with ultrasound, measurement of thyroglobulin levels (blood test), and in some cases iodine 131 total body scanning. Other radiology exams, PET scan, CT or MRI imaging, may be used in cases where iodine-131 uptake is not present.