Recurrent Thyroid Cancer

The clinical course of patients with thyroid cancer is unpredictable. Numerous studies, however, have documented that patients can be classified into groups at low or high risk for recurrence or death on the basis of age, gender, tumor size, histology, and extent of local invasion as well as the presence or absence of distant metastases.1 Resectability and extent of resection, with the adjuvant use of iodine 131 and thyroid-stimulating hormone (TSH) suppression therapy, also influence outcome.

The various scoring systems such as AGES (age, grade, extent, and size), AMES (ages, metastases, extent, and size), and TNM (rumor, node, metastasis) attempt to identify prognostic factors of tumor behavior for recurrence and survival.1

Goiter, or thyroid nodules, occur in 4% to 6% of women and in 2% of men in North America; clinical thyroid cancer, however, occurs only in about 40 persons per million.2 A selective approach, therefore, must be used to determine who will benefit from thyroidectomy and who can be safely observed or treated with thyroid hormone. If this selection process is not judicious, there will be delays in diagnosis and an adverse outcome. Earlier diagnosis of thyroid cancer, in the much larger number of patients with goiter, has a considerable impact on both the recurrence and the survival rate of patients with thyroid cancer.

Recurrent thyroid cancer after treatment may be local, regional, or distant. Local recurrence is related both to the invasiveness of the cancer at presentation and to the surgical procedure used for the eradication of the malignant tissue. Extracapsular invasion and multicentricity of the tumor are determinant factors that also need to be considered. Unfortunately, these factors usually cannot be ascertained preoperatively to determine the extent of the resection. In high-risk patients, recurrence is common (-30%), and treatment of recurrence is less successful.3,4 Because one cannot precisely predict tumor behavior, we favor total thyroidectomy for most patients with thyroid cancer when this operation can be safely performed. Just as the expression "no acid, no ulcer" is generally accepted in patients with peptic ulcer disease, the notion that "no tissue left, no local recurrence" may also be valid. In patients with clinical thyroid cancer, local recurrence may occur in the residual thyroid tissue, in the thyroid bed, or in the immediately adjacent area, excluding lymph nodes. An insufficient thyroidectomy, failure to remove all the thyroid, and the cancer may be responsible for some recurrences; microscopic extension into the adjacent tissue accounts for the remainder.

The results of thyroidectomy are well documented in the study of 963 papillary thyroid cancer patients at the Mayo Clinic by Grant and associates.5 The risk of cancer death with a local recurrence located outside the thyroid remnant was much greater than with a remnant recurrence alone. Practically, however, the exact type of this kind of recurrence, whether in residual tissue or in thyroid bed and adjacent tissues, is often difficult to determine when the recurrent tumor has reached appreciable size. Of concern also is that even patients judged to be at low risk have about a 15% recurrence rate, and at least 33% of these patients die from their thyroid cancer.1,3

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