eMedicine Specialties > Oncology > Carcinomas of Endocrine Organs

Hurthle Cell Carcinoma

Author: Serhat Aytug, MD, Staff Physician, Division of Endocrinology, Diabetes and Metabolism, CrystalRun Healthcare
Coauthor(s): Lawrence E Shapiro, MD, Chief, Division of Endocrinology and Metabolism, Professor of Medicine, Department of Medicine, Winthrop University Hospital
Contributor Information and Disclosures

Updated: Jul 21, 2008

Introduction

Background

Hürthle cell carcinoma of the thyroid gland is an unusual and relatively rare type of differentiated thyroid cancer. Hürthle cell cancer accounts for only about 3-10% of all differentiated thyroid cancers; therefore, few institutions have extensive experience with Hürthle cell neoplasms. According to the World Health Organization (WHO), these neoplasms are considered a variant of follicular carcinoma of the thyroid and are referred to as follicular carcinoma, oxyphilic type.

Oncocytic cells in the thyroid are often called Hürthle cells, and oncocytic change is defined as cellular enlargement characterized by an abundant eosinophilic granular cytoplasm as a result of accumulation of altered mitochondria. This is a phenomenon of metaplasia that occurs in inflammatory disorders, such as thyroiditis, or other situations that result in cellular stress. The proliferation of oncocytes gives rise to hyperplastic and neoplastic nodules.¹  

The cytological features for Hürthle cell neoplasms are hypercellularity with a predominance of Hürthle cells (usually >75%), few or no lymphocytes, and scanty or absent colloid. In 1898, Askanasy described Hürthle cells; however, they are mistakenly named for the German physiologist who actually described the interfollicular C-cell.² Hürthle cells are large and polygonal in shape, with indistinct cell borders. They have a large pleomorphic hyperchromatic nucleus, a prominent nucleolus, and intensely pink, fine, granular cytoplasm with hematoxylin-eosin staining. Hürthle cells are also found in other tissues, such as the salivary gland, parathyroid gland, esophagus, pharynx, larynx, trachea, kidney, pituitary, and liver.

Controversy exists about the origin of Hürthle cells, which generally are thought to derive from the follicular epithelium. A Hürthle cell neoplasm is defined generally as an encapsulated thyroid lesion consisting of at least 75% of Hürthle cells. Distinguishing a benign neoplasm from a malignant neoplasm based on cytologic analysis of fine-needle aspiration (FNA) biopsy is not possible. Features such as pleomorphism, anaplasia, hyperchromatism, and atypia are also observed in benign follicular adenomas; therefore, a definitive way to differentiate Hürthle cell carcinoma from Hürthle-cell adenoma is based on vascular invasion and/or capsular invasion, as well as on permanent histologic sections or extrathyroidal tumor spread and lymph node and systemic metastases.

Incidence of malignancy in patients with Hürthle-cell neoplasms reported in the literature is variable. Reports show that malignancy occurs in 13-67% of patients. Overall, only about 33% of Hürthle cell tumors demonstrate signs of that invasive growth that indicates malignancy and the possibility of metastasizing. On balance, Hürthle cell tumors may be considered to be more likely to metastasize than follicular tumors. The likelihood of nodal metastases is greater in Hürthle cell tumors than in follicular tumors; it is, however, not as great as with papillary tumors.

Some lesions considered malignant could be a reflection of permissive histologic interpretation, which may lead to the inclusion of non-neoplastic Hürthle cell lesions with malignant tumors. Obviously, this factor has a major impact in interpreting the natural history of this disease and adds to the controversy about the aggressiveness of Hürthle cell carcinoma. This leads to reported overall mortality rates ranging from 9-28%.

Tumor size is an important feature for biological behavior. A 1988 study found that a Hürthle tumor that is 4 cm or larger has an 80% chance of histologic evidence of malignancy.³ In another study by Pisanu et al,⁴ in a series of 23 patients, the mean tumor size was significantly greater for carcinomas than adenomas (3.1 cm vs 1.9 cm).

In another study done at Memorial Sloan-Kettering Cancer center,⁵ outcomes of 56 patients with Hürthle cell cancer were analyzed. In this study, recurrence was a significant predictor of tumor-related mortality, and the most significant predictor of outcome was extent of invasion. In addition, tumor size, extrathyroidal disease extension, and initial nodal or distant metastasis were found to be associated with an adverse outcome.

Hürthle cell cancer has the highest incidence of metastasis among the differentiated thyroid cancers. Metastatic disease is reported at the time of initial diagnosis in 10-20% of patients and in 34% of the patients overall. Metastatic disease is usually hematogenous, but lymph node metastasis is also not uncommon and more frequently involves the regional lymph nodes. Some studies arguably show that lymph node metastases at initial diagnosis may not be an unfavorable prognostic factor. The lungs, bones, and central nervous system are the most prevalent sites of metastases.

Pathophysiology

No widely accepted paradigm exists for the pathogenesis of follicular and Hürthle cell cancer of the thyroid. Some evidence suggests that a multistep adenoma-to-carcinoma pathogenesis may be present; however, this concept is not universally accepted. Many of the cells probably develop from preexisting adenomas, but a follicular carcinoma in situ is not recognized pathologically.

Progressive transformation through somatic mutations of genes that are important in growth control are involved in follicular thyroid cancer formation. Low iodide intake is a key environmental factor determining the relative incidence of follicular and papillary cancers. Most follicular adenomas and all follicular carcinomas are thought to have monoclonal origin.

Oncogene activation, particularly by mutation or translocation of the ras oncogene, is common in both follicular adenomas and follicular thyroid carcinomas (around 40%), supporting a role in early tumorigenesis. Such ras oncogene mutations are not specific for follicular tumors and also occur in papillary thyroid cancer (PTC). The ras oncogene is frequently involved in the pathogenesis of Hürthle cell tumors. In papillary thyroid cancers and in many Hürthle cell tumors, RET rearrangements are found; these are not found in follicular tumors. Local spread may be found in RET- positive cases; RET- negative cases, as in follicular cancer cases, are more likely to spread through blood to distant metastatic sites.

An association also was found between overexpression of the p53 gene product and a subset of Hürthle cell carcinomas. Reduced immunoexpression of E-cadherin exists, with a trend to a diffuse cytoplasmic pattern, both in benign and malignant Hürthle cell tumors and in papillary, poorly differentiated, and undifferentiated thyroid carcinomas. Isolated studies indicate overexpression of the N-myc oncogene, tumor growth factor (TGF)-alpha, TGF-beta, insulinlike growth factor (IGF)-1, and somatostatin receptor in Hürthle cell carcinomas.

Cytogenetic abnormalities and evidence of genetic loss are more common in follicular thyroid cancer than in papillary thyroid cancer. These abnormalities occur in follicular adenomas, suggesting that cell cycle control, mitotic spindle formation, DNA repair, or more than one of these mechanisms may be impaired in these neoplasms, possibly at an earlier stage.

Activating mutations of genes encoding the thyrotropin receptor and the alpha subunit of the stimulatory G protein are also reported in some follicular carcinomas. These losses are associated particularly with chromosomes 3, 10, 11, and 17. The deletions and/or rearrangements involving the p (short) arm of chromosome 3 are the most common. Loss of a tumor suppressor on chromosome arm 3p has been postulated to be specific for follicular thyroid cancer and may be involved in adenoma-to-carcinoma progression.

Restriction fragment length polymorphism (RFLP) analysis demonstrates that unbalanced losses of genetic material are relatively common in Hürthle cell neoplasms. Loss of heterozygosity from the q (long) arm of chromosome 10 is also detected in oncocytic tumors. Evidence suggests that some Hürthle cell adenomas and carcinomas can express an RET/PTC gene arrangement, which is more unique to papillary thyroid carcinoma.

Because of this gene arrangement, Hürthle cell neoplasms supposedly have another subclassification, namely the papillary variant of Hürthle cell cancer (ie, Hürthle cell papillary thyroid carcinoma), in addition to Hürthle cell cancer and adenoma. Clinically, this group of tumors tends to behave like papillary thyroid carcinoma; however, they are more indolent, with a propensity for lymph node metastasis rather than hematogenous spread. In 2006, Maxwell et al reported that the Hürthle cell tumors with RET/PTC - positive gene arrangement have higher incidence of regional metastatic disease and more aggressive treatment has been recommended.⁶

As reported by Asa, many Hürthle cell tumors, whether benign or malignant, show papillary change. This is a pseudopapillary phenomenon because Hürthle cell tumors have only scant stroma and may fall apart during manipulation, fixation, and processing. True oxyphilic, or Hürthle cell, papillary carcinoma has been reported to comprise 1-11% of all papillary carcinomas. These tumors have a papillary architecture but are composed predominantly, or entirely, of Hürthle cells.¹

Mitochondrion-related alterations, such as mutations in mitochondrial DNA, are also described in Hürthle cell tumors. Defects of cytochrome c oxidase and the deletion of mitochondrial DNA occur frequently in Hürthle cell tumors and in Hürthle cells of Hashimoto thyroiditis. In one study, almost all Hürthle cells displayed a common deletion, somatic mitochondrial point mutations, or both.⁷ Activating gene mutations encoding the thyrotropin receptor and the alpha subunit of the stimulatory G protein are also reported in some follicular carcinomas.

DNA content profiles after flow cytometry are commonly abnormal. Hürthle cell neoplasms, including histologically benign tumors, are often aneuploid. This finding parallels with nuclear atypia and anisocytosis. The demonstration of aneuploidy may be a marker for a particularly aggressive clinical behavior compared to euploid tumors. In a recent Italian study, p27 and cyclin D3 proteins were found to be overexpressed in Hürthle cell carcinoma cell lines and clinical samples of thyroid cancer.^8,9 The accumulation of p27 was found to be associated to the overexpression of cyclin D3 in Hürthle cell carcinoma of the thyroid.

Frequency

United States

Thyroid cancer is uncommon, and, among all cancers, it accounts for 0.74% in men and 2.3% in women. The average age-adjusted annual incidence for thyroid cancer is less than 40 cases per 1 million people. Among thyroid neoplasms, Hürthle cell carcinomas account for about 3-10% of these cancers.

For thyroid cancers as a whole, in the US for 2007, the projected new thyroid cancer cases are 33,550 for both sexes, and of these, 25,480 are in females and 8,070 are in males. The estimated deaths are 2,320 for both sexes, 1,030 in males and 1,290 are in females. It is reasonable to estimate that Hürthle cell cancer cases will be about 3-10% of these.¹⁰

International

Worldwide frequency likely approximates that of the United States. In general, the annual incidence rate of thyroid cancer in various parts of the world is 0.5-10 cases per 100,000 population. Approximately 3-10% of these cases are Hürthle cell carcinomas.

Mortality/Morbidity

Hürthle cell cancer reportedly behaves in a more aggressive fashion than other well-differentiated thyroid cancers, with a tendency to higher incidence of metastasis and a lower survival rate. This is truer for the lesions that are clearly demonstrated to be malignant and in patients who are considered to be at high risk based on such factors as age, tumor size, invasiveness, and the presence of metastasis. Widely invasive tumors behave more aggressively. Recurrence among patients with Hürthle cell carcinoma is considered to be incurable.

Ghossein et al at Memorial Sloan Kettering Cancer center reported that in encapsulated ("minimally invasive") Hürthle cell carcinomas, the extent vascular invasion strongly correlated with recurrence. Also, presence of mitosis and a solid/trabecular tumor growth pattern also correlated with higher risk of recurrence.¹¹

• Mortality rates vary in different series, based on the staging systems used, which consider the patient's age, tumor size, extrathyroidal tumor spread, pathologic classification of the neoplasm (Hürthle cell carcinoma versus adenoma), and the therapeutic approach.
• Overall survival rates reportedly are similar or worse in patients with Hürthle cell carcinoma compared with rates for persons with follicular carcinoma. In a case series of Hürthle cell carcinoma, mortality rates determined at 5, 10, and 20 years were reported at 8%, 18%, and 33%, respectively. Two other case series confirmed a 20-year cause-specific mortality rate of 20-35%. One study showed that when distant metastases were present, the 5-year mortality rate was 65%.¹² Another study involving 33 patients showed that disease-free survival was 65% in 5 years and 40.5% in 10 years.¹³
• Morbidity depends on the behavior of the Hürthle cell carcinoma.

Race

Studies do not usually reflect racial differences; all races appear to be affected equally.

Sex

See Frequency.

Age

The age range of patients presenting with this condition is 20-85 years. The mean age is usually 50-60 years, approximately 10 years older than the age associated with other types of differentiated thyroid cancers.

Clinical

History

• History in patients with a thyroid nodule or a known follicular or Hürthle cell neoplasm is neither sensitive nor specific for a diagnosis of malignancy; however, certain clinical features are more suggestive of malignancy, as follows:
• A palpable mass in the thyroid (most common clinical sign)
• Symptoms of pressure more suggestive of malignancy (eg, dysphagia, dyspnea, coughing, choking spells, hoarseness)
• Rapid growth or significant compressive symptoms
• Pain
• Hürthle cell carcinoma is more often multifocal and bilateral.
• Lymph node metastasis and symptoms confined to metastatic sites can be the first clinical presentation in a subgroup of cases.
• Prior history of head and neck external beam irradiation can be present and should alert the clinician of a possible malignancy. Multifocal and bilateral disease is more common. A family history of thyroid cancer and endocrinopathies can also be present.
• Patients are usually euthyroid, but, in a small percentage of patients, hyperthyroidism or hypothyroidism can be present.
• Other benign thyroid and parathyroid disorders can be observed, as follows:
• Graves disease
• Colloid nodular disease
• Lymphocytic thyroiditis
• Thyroid hyperplasia
• Parathyroid adenoma
• Follicular adenomas

Physical

The most common physical examination finding is a palpable single neck mass. Multiple masses can also be palpated.

• The contralateral lobe can also harbor malignancy given the increased risk of bilateral disease.
• Regional lymph nodes are not as commonly involved as in papillary carcinoma but can be felt in the neck region and locoregionally.
• The trachea can be compressed and deviated secondary to the mass effect of the tumor. Hoarseness can occur if vocal cord involvement is present.
• Horner syndrome can be present from involvement of the cervical sympathetic ganglia.
• If the tumor extends into the upper mediastinum behind the sternum, the superior mediastinal syndrome may ensue with facial swelling, and dilated veins can be observed.
• A hard fixed thyroid nodule, cervical lymphadenopathy, and vocal cord paralysis are features that may indicate carcinoma.
• Physical findings of metastases and pathologic bone fractures can also be found in long and flat bones.
• Most patients with Hürthle cell cancer and Hürthle cell adenomas are euthyroid. Signs of thyrotoxicosis, although rare, can be present. Either massive tumor burden or functioning metastatic disease causes thyrotoxicosis.

Causes

• History of radiation to the neck
• Iodide deficiency
• Overexpression of the p53 oncogene
• Activating mutations of genes encoding the thyrotropin receptor and the alpha subunit of the stimulatory of G protein are reported in some follicular carcinomas.
• Somatic mutations of genes important in growth control
• Oncogene activation, particularly by mutation or translocation of the ras oncogene
• Mitochondrion-related alterations (eg, mutations in mitochondrial DNA) also are described.
• In a recent study by Maximo et al, somatic and germline mutation in GRIM-19, a dual function gene involved in mitochondrial metabolism and cell death, is linked to Hürthle cell tumors of the thyroid. This is the first nuclear gene mutation described for a subgroup of Hürthle cell carcinomas.¹⁴

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