Clinical Features

Anaplastic cancer affects women and men in a ratio of 1.0:1.5.2 The peak incidence of this disease occurs in the seventh decade of life (mean, 64 years).1'2 It is unusual for patients younger than 40 years to be affected by this disease, and when it occurs one should question the reliability of the diagnosis.

Radiation exposure has been documented but does not seem to have a critical role in pathogenesis. Patients usually present with a rapidly enlarging, bulky, thyroid mass12,5 that is firm to hard and frequently fixed. There may be a variation in the extent of anaplasia because some thyroid tumors may show small areas of dedifferentiation, which would still qualify them in the consideration of anaplastic cancer. However, such cases usually do not pose the same problem or have the dire outlook of the diffusely involved gland. Anaplastic cancer may compress the trachea and infiltrate the skin, causing overlying necrosis. Lymph node enlargement is frequent (84%) and early.12 The tumor extends to and becomes fixed to the larynx, esophagus, and carotid vessels. Vocal cord paralysis can occur because of tumor infiltration of the recurrent laryngeal nerve or vocal cord, and glottic obstruction is of concern. Obstruction of the superior vena cava can be seen in more extensive cancer, particularly when there is a retrosternal component.

Symptoms such as dysphagia, dysphonia, and dyspnea are common.12'5 Systemic metastases occur in 75% of patients and usually involve lung (more than 80%) as well as bone and brain (15%), adrenal glands (33%), and intra-abdominal nodes (17%).''2

Investigation can vary and depends on the circumstances of the individual patient. Thyroid function tests are usually normal, but with a rapidly growing tumor, evidence of at least incipient compensated hypothyroidism can be seen by virtue of an elevated thyroid-stimulating hormone serum level by sensitive assay. Scintiscan of the thyroid gland shows a classic cold area at the site of the tumor. Chest x-ray film and computed tomography scan can demonstrate extrathyroidal extension and invasion.

Diagnosis can be established by fine-needle aspiration biopsy (FNAB).4-7 Scandinavian authors adamantly prefer FNAB for tissue diagnosis because they view incisional biopsy as associated with poor healing, delay of treatment, and acceleration of tumor growth.4'7 The diagnosis of anaplastic cancer must be differentiated from that of lymphoma and poorly differentiated medullary carcinoma, and appropriate immunophenotyping and other marker examinations may be required.

DNA cytometry of anaplastic cancer usually shows an aneuploid picture indicative of a poor outlook. Other thyroid investigational imaging procedures such as ultrasonography, computed tomography scan, and magnetic resonance imaging document the limits of the imaging of a mass and sometimes extensive invasion but cannot establish the tumor histology. Somatostatin scans are occasionally positive in ATC and in other thyroid cancers. Positron emission tomography scans are unreliable in ATCs but appear to be positive in patients with poorly differentiated thyroid cancer that does not take up radioiodine.21

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