The contemporary management of well-differentiated thyroid cancer requires a multidisciplinary approach involving primary care physicians, endocrinologists, surgeons, pathologists, nuclear medicine specialists, and sometimes radiologists and oncologists for diagnosis, treatment, and long-term surveillance. Well-differentiated thyroid carcinoma includes papillary and follicular thyroid carcinomas. These two types of cancer comprise approximately 85% to 90% of all thyroid malignancies. Managing these cancers raises common concerns that will be addressed later.
Despite the fact that most cases of well-differentiated thyroid carcinoma have an excellent prognosis, optimal treatment of the disease remains controversial. Perhaps because of the slow growth of the tumors and the infrequency with which patients die of the disease, no studies have been large enough or of long-enough duration to definitively answer some of the central questions in the treatment of well-differentiated thyroid cancer. The optimal extent of surgical resection continues to be debated, as does the question of which patients should receive radioactive iodine(Drug information on iodine). Various authors have questioned whether a lymph node dissection is beneficial to patients, and if so, how extensive such a dissection should be.
Regardless of the answer to these questions, most patients with well-differentiated thyroid cancer will do well, but only a large study with several decades of follow-up will be able to discern any advantages among the treatment options presented above. To date, there have been no randomized studies to evaluate the comparative benefits of various treatment modalities.
Most patients with well-differentiated thyroid cancer initially present with a thyroid nodule. The role of the primary care physician is critical at this stage, because the majority of patients are diagnosed only after a nodule is palpable on physical examination. Nevertheless, the increasing use of diagnostic imaging such as carotid duplex scanning and computed tomography (CT) scanning (for other reasons) has led to more frequent identification of thyroid nodules before they are palpable.
Once a nodule is identified, the appropriate diagnostic work-up includes a careful history with attention to risk factors such as radiation exposure, previous thyroid cancer, or less commonly, family history of well-differentiated thyroid cancer. Hoarseness or lymphadenopathy associated with a palpable thyroid mass is particularly suspicious for carcinoma.
Numerous imaging modalities are available for evaluating thyroid nodules. In most instances, an ultrasound of the neck will provide accurate and detailed information about the nodule as well as the status of the remainder of the thyroid, including any possible lymphadenopathy in the cervical region. Increasingly, microcalcifications in association with a thyroid nodule have been identified as suspicious for papillary thyroid carcinoma.
Thyroid scintigraphy continues to be helpful if the functionality of a nodule is being questioned. CT scanning and magnetic resonance imaging (MRI) are generally less helpful in the initial evaluation. Positron-emission tomography (PET) scanning in conjunction with fluorine-18 fluorodeoxyglucose (FDG) has shown promise in identifying thyroid malignancies, but it is not yet clear what the most appropriate role for this imaging modality will be.[4,5]
A diagnosis of well-differentiated thyroid cancer is often made preoperatively with the use of fine-needle aspiration (FNA) cytology. A diagnosis of papillary thyroid carcinoma is readily made on cytologic evaluation. The cells characteristically have enlarged nuclei with dense chromatin and, frequently, intranuclear cytoplasmic inclusions.
The cytologic diagnosis of follicular thyroid carcinoma is more problematic. The distinction between benign adenoma and malignant carcinoma for this type of tumor is not based primarily on cellular features, but rather, on the presence of capsular or vascular invasion. In other words, the cells in a benign follicular adenoma and a malignant follicular carcinoma may be identical. The distinction between benign and malignant depends largely on where the cells are located. If there is no capsular or vascular invasion, then the lesion is considered benign.
The nature of this distinction often leads to an indeterminate cytologic evaluation, even when a follicular thyroid carcinoma has been aspirated. Such nodules are usually characterized as "follicular neoplasms," since benign lesions cannot be distinguished from malignant lesions on the basis of cytology alone. When the results of the aspiration are indefinite, and because the issue of capsular or vascular invasion cannot be determined no matter how many times the cells in a nodule are sampled, most physicians recommend at least a partial thyroidectomy (lobectomy or hemithyroidectomy). Only after the pathologist has completely evaluated the entire nodule for capsular and vascular invasion can such a tumor be categorized as a benign follicular adenoma.
Hürthle Cell Neoplasm
Follicular neoplasms can be further subcategorized into Hürthle cell neoplasms. These uncommon tumors consist of large acidophilic or oncocytic cells. Some authors have suggested that Hürthle cell carcinomas have a worse prognosis than the usual follicular carcinoma.[7,8] This finding may be related to the greater likelihood that Hürthle cell carcinomas are locally invasive and concentrate radioiodine less avidly.