Anaplastic Thyroid Cancer
Anaplastic thyroid carcinoma (ATC), also known as undifferentiated carcinoma, is a rare, highly aggressive malignant tumor accounting for 2% to 3% of all thyroid gland neoplasms. Anaplastic thyroid carcinoma continues to rank as one of the most deadly diseases worldwide and carries a very poor prognosis. In addition to considerable local invasion, anaplastic thyroid carcinoma often presents with metastatic spread to regional lymph nodes and distant sites. Due to the aggressive nature of this type of cancer, the mortality is close to 100 percent and typically, patients already have metastatic disease by the time of diagnosis. However, recent advances in understanding the genetic and molecular pathogenesis of ATC hold promise for targeted therapy for this disease.
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The risk factors of ATC, according to a case-control study by Zivaljevic et al., included low education level, type B blood group, and goiter.Moreover, patients with poorly-differentiated thyroid cancer with the following characteristics tend to present with more complicated and adverse clinicopathological findings; 1. older age, 2. male patient, 3. advanced locoregional disease, and 4. distant metastases.
The frequency of anaplastic thyroid carcinoma is higher in areas of endemic goiter. Anaplastic thyroid carcinoma is responsible for 1.7% of all thyroid cancers in the United States. However, geographical prevalence ranges from 1.3% to 9.8%. Patients are typically elderly (sixth to seventh decades of life); the mean age at diagnosis is 65 years, and the female-to-male ratio is 2 to 1. According to the epidemiological data derived from the surveillance, epidemiology, and results (SEER) database, the incidence of anaplastic thyroid cancer was steady between 1973 and 2002.
Approximately 20 percent of patients with ATC have a history of differentiated thyroid cancer. Up to 30 percent of ATC may have associated synchronous differentiated cancer.  The majority of the synchronous thyroid tumors are papillary cancer, but follicular types have also been reported. The transformation from differentiated to anaplastic cancer has also been described.  Tp53 gene inactivation may play an important role in the progression from differentiated to undifferentiated carcinoma. Thyroid-specific rearrangements RET/PTC and PAX8/PPARγ are rarely found in poorly differentiated or undifferentiated thyroid cancer, suggesting that these genetic alterations do not predispose cells to dedifferentiation
The cytogenetics are often complex and show progressive accumulation of chromosomal alterations (numerical and structural aberrations). The following gene mutation is commonly reported in ATC: p53 (most common), RAS, BRAF, β-catenin, PIK3CA, Axin, APC, and PTEN.
- Bulky mass (mean: 6 cm)
- Homogeneous and variegated appearance
- On cut section: light tan and fleshy with zones of necrosis and hemorrhage
- Infiltrating, often into adjacent soft tissues and organs
The highly variable microscopic appearances of anaplastic thyroid carcinoma are broadly categorized into three patterns, which can occur singly or in any combination:
- Giant cell
- The sarcomatoid form is malignant spindle cells with features commonly seen in high-grade pleomorphic sarcoma.
- The giant cell form is composed of highly pleomorphic malignant cells, some of which contain multiple nuclei.
- The epithelial form manifests squamoid or squamous cohesive tumor nests with abundant eosinophilic cytoplasm; occasional keratinization can be present.
Common to all three forms are necrosis, an elevated mitotic rate, and an infiltrative growth pattern. Vascular invasion is also often present.
Immunohistochemistry helps to distinguish anaplastic carcinoma from other undifferentiated malignancies using CD45 and other lymphoid markers along with melanocytic markers to exclude lymphoma and melanoma, respectively.
Common thyroid-lineage markers such as TTF1 and thyroglobulin are usually absent, whereas PAX, also a thyroid-lineage marker, is retained in approximately half of all cases. Positive cytokeratin expression supports the epithelial nature of anaplastic thyroid carcinoma, but negative immunostaining for cytokeratin does not exclude the diagnosis.
History and Physical
The most common clinical presentation of anaplastic thyroid carcinoma are:
The most common ultrasonographic findings of anaplastic thyroid carcinoma include:
- Solid masses
- Marked hypoechogenicity
- Irregular margin
- Internal calcification
- Wider than tall shape
- Cervical lymph node involvement
Fine Needle Aspiration (FNA)
A fine-needle biopsy is a useful diagnostic modality. However, the diagnosis of anaplastic carcinoma must be established by surgical biopsy or during surgery.
Cytologic findings of anaplastic thyroid carcinoma include:
- Biphasic population: tumor and uninvolved thyroid
- Highly cellular with single cells and focal clusters composed of remarkable atypical cells
- Mitotic figures are prominent
- Background necrosis and inflammatory cells may be present
Intraoperative Frozen Section and Pathology Consultation
Intraoperative consultation provides a rapid diagnosis to determine the ongoing operative extent and approach.
Computed Tomography Scan
Anaplastic thyroid carcinomas usually present as large isodense or slightly hyperdense masses relative to skeletal muscle. Calcification and necrosis are present and often are extensive. A computed tomography scan is useful in defining the local extent of anaplastic thyroid carcinoma and detecting lymph node metastases.
Magnetic Resonance Imaging
Magnetic resonance imaging can be useful to best assess tumor extension, particularly in the esophagus musculature, trachea, and carotid vessel.
F-fluorodeoxyglucose Positron Emission Tomography (FDG-PET)
Staging assessment with F-fluorodeoxyglucose positron emission tomography (FDG-PET) fused coincident computerized tomography scan (FDG-PET/CT) is uniquely valuable in anaplastic thyroid carcinoma due to its enhanced expression of glucose transporter (GLUT-1), resulting in increased glucose uptake.
Treatment / Management
The recommended treatment for anaplastic thyroid carcinoma is based on surgery when feasible and chemoradiation either concurrently or sequentially. Most cases of anaplastic thyroid carcinoma are unresectable at presentation because of the invasion of cervical structures. Surgery should aim to secure the patient’s airway.
Debulking surgery is the most common procedure in anaplastic thyroid carcinoma. It consists of removing any gross tumor that is potentially threatening the airway with the aim of preserving the larynx. However, a tracheostomy may be necessary in cases of airway compromise. While complete excision is often impossible due to the local extension of the disease, the quality of resection is a significant prognostic factor for survival.
Radiation Therapy and Chemotherapy
External-beam irradiation is effective in improving local control. For patients with locally advanced unresectable disease, definitive radiation therapy and chemotherapy are the recommendations. Adjuvant radiation therapy should be performed in all cases, including completely resected small-size incidental anaplastic thyroid carcinoma and anaplastic thyroid carcinoma with a differentiated component.
Anaplastic thyroid carcinoma is usually not responsive to I131 therapy. Radioiodine is only a recommendation upon identification of a differentiated iodine-positive component. New insights into biological behavior and the genetic and molecular pathogenesis of anaplastic thyroid carcinoma might offer novel targeted therapies.
Histological differential diagnosis:
- Metastatic disease to the thyroid, including metastatic clear-cell renal carcinoma
- Primary thyroid lymphoma
- Primary thyroid sarcoma
- Poorly differentiated thyroid carcinoma
- Squamous cell thyroid carcinoma
- Medullary carcinoma
Management of anaplastic thyroid cancer includes expedited staging and tissue sampling with biopsy or fine-needle aspiration to detect next-generation molecular sequencing.
Thyroid carcinomas staging is according to the 8th edition of the American joint committee on cancer (AJCC) classification. According to the International Union Against Cancer (UICC)—TNM staging and AJCC system, all anaplastic thyroid carcinomas are considered stage IV. Stage IVA and IVB patients have intrathyroidal tumors (IVA) and extrathyroidal tumors (IVB) and no distant metastatic disease, whereas stage IVC patients have distant metastasis.
Anaplastic thyroid carcinoma is poorly responsive to any multimodality therapy. The most recent Surveillance, Epidemiology, and End Results database analysis (1986-2015) reported median survival of 4 months and a 6-month OS of 35%. Survival beyond 2 years is 12%.
- Younger age (less than or equal to 60 years old)
- An absence of cervical or distant metastases
- Small tumors (less than or equal to 5 to 7 cm)
- Unilateral tumors
- An absence of local invasion of the surrounding tissue or nodal involvement
- An incidental finding of anaplastic thyroid carcinoma within a thyroidectomy specimen
Local invasion of the surrounding structures occurs in almost 70% of patients as observed in large series: muscles (65%), trachea (46%), esophagus (44%), laryngeal nerve (27%), and larynx (13%). Lymph node metastases are a feature in almost 40% of patients.
The progression of anaplastic thyroid carcinoma is rapid, and most patients die from local airway obstruction or complications of pulmonary metastases within one year. Metastases occur in up to 75% of patients. They most frequently involve the lungs (80%), the brain (5 to 13%), and bones (6 to 15%).
Pearls and Other Issues
To avoid the development of anaplastic carcinoma, longstanding goiters, as well as benign nodules, should be followed carefully and considered for resection if they grow or do not respond to medical therapy. Moreover, total thyroidectomy for malignant disease can prevent the development of anaplastic carcinoma.
Enhancing Healthcare Team Outcomes
Due to the aggressive nature of the disease, prompt diagnosis is critical in determining appropriate treatment options. Management of anaplastic thyroid carcinoma is complex and needs an interprofessional team approach involving a team that consists of an ENT surgeon, a surgical oncologist, a radiation oncologist, a pathologist, an endocrinologist, a radiologist, and a nuclear medicine specialist. The pharmacist reviews prescribed medications to provide patient education and monitors compliance. Oncology pharmacists assist in planning chemotherapy and provide feedback to the team. Specialty trained otolaryngology and oncology nurses help coordinate care, educate patients and their families, schedule follow up, and inform the team of status changes. Palliative care and hospice nurses and doctors are commonly involved in improving end-of-life care. [Level 5]
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