THYROID CARCINOMA



Thyroid cancer is a relatively rare disorder (4 in 100,000]. Furthermore, most varieties of thy­roid cancer are of low-grade malignancy. Papil­lary or follicular carcinomas constitute about 90 per cent of all thyroid cancers. Anaplastic and medullary carcinoma accounts for the remainder.

Papillary carcinoma generally presents as a thy­roid nodule that may be associated with local in­vasion and lymph node spread. The size of the initial lesion (>2.5 cm) and the presence of lymph node involvement adversely influence the recur­rence rate and long-term prognosis. Follicular car­cinoma is more aggressive and frequently presents with metastases, especially to the lung, bone, or brain. The size of the initial lesion does not in­fluence prognosis. In many cases the small thy­roid primary is overlooked and is diagnosed in retrospect following examination of the meta­static tissue. Both of these cancers have a low re­currence rate and a relatively good prognosis.

Primary therapy entails total thyroidectomy with nodal dissection followed in most cases (six weeks postoperatively) by 131I ablative therapy for any remnant tissue. Irradiation is probably not in­dicated for small (<2.5 cm), noninvasive papil­lary lesions. Both surgical and radioactive abla­tive therapies are followed with T4 suppression of TSH. Measurement of serum thyroglobulin has no pretherapeutic diagnostic value. It is, however, an excellent way to determine the effect of treat­ment and to monitor for recurrence.

Anaplastic carcinoma predominantly affects older individuals (>50 years). It is very aggressive and rapidly induces pain and symptoms related to local pressure (dysphagia, hoarseness). Death generally occurs within 12 months, but surgically resectable disease may have a better prognosis, with a five-year survival of approximately 30 per cent.

Medullary carcinoma, which develops^ in the parafollicular cells (C cells), may be sporadic or familial (autosomal dominant). When familial, it is frequently a component of a multiple endocrine neoplasia syndrome (MEN Type II). This tumor produces calcitonin; measurement of basal serum calcitonin can substantiate its presence. Provoc­ative testing with calcium or pentagastin (calci­tonin response) may detect early C-cell hyperpla­sia in subjects at risk (MEN Type II families). Surgical excision of the primary lesion in the absence of nodal involvement produces an excellent prognosis (90 per cent survival at 10 years). In contrast, patients with nodal disease have only a 40 per cent survival at 10 years.

One of the most important factors in the eval­uation of a patient with suspected thyroid cancer (thyroid nodule) is a history of low-dose irradia­tion (<500 rads) to the head or neck area during childhood. Such individuals are at high risk for thyroid cancer. Careful investigation of such pa­tients will detect follicular or papillary carcinoma in about 30 per cent of cases. It is now recom­mended that irradiated patients have a thyroid (clinical) examination at two-year intervals. In the absence of palpable disease, laboratory evaluation is not warranted. Postirradiated patients- with a palpable dominant nodule should receive total thyroidectomy with removal of nodes if there is metastatic disease. If invasive carcinoma is present, postoperative remnant ablation with 131I should be carried out at six weeks. Suppressive therapy with T4 will be necessary for life.





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