The incidence of thyroid cancer is growing, partially due to increased awareness and better diagnostic evaluations. According to American Cancer Society statistics, there were about 56,460 new cases diagnosed in 2012. Thyroid cancer diagnoses in the United States have doubled since 1990 but the mortality rate has remained about the same. In 2012, about 1,780 thyroid cancer deaths occurred.
In a publication from the Surveillance and End Results (SEER) database, the rising frequency of differentiated thyroid cancers was reported as being due to increasing detection, not necessarily as a result of increasing occurrences. Others believe this does not explain the increased incidence in developing countries in which the availability and quality of medical care has not risen to the level that would account for the rise in the number of diagnosed cases.
The ultrasound, especially in the hands of a thyroid specialist, has allowed us to image small thyroid nodules that otherwise might have been overlooked. Characteristics of the nodule, as well as size, allow us to better formulate the diagnostic and therapeutic course. Prompt detection and evaluation by means of an ultrasound-guided fine needle aspiration has allowed us to make decisions based on the cytopathology results, rather than having to subject the patient to more invasive surgical procedures, including hemithyroidectomies and total thyroidectomies.
Unfortunately, the cytology results sometimes (10-15 percent) are not diagnostic of either thyroid cancer or a benign nodule. Up to now, nodules that are suspicious for being follicular or Hürthle cell adenomas are further classified as being benign or malignant by examining the entire surgical specimen. Patients require further studies often are subjected to surgery only to find out the nodule is benign. The risk of malignancy, depending on the ultrasound characteristics and other clinical findings, is between 20 and 35 percent. Certain genetic (molecular) markers are being evaluated to help minimize the necessity for surgery. Molecular testing of the aspirate may help in narrowing the odds, and there are certain situations in which it can assist in the decision making, but there needs to be more clinical studies completed before it is considered for routine use.
Treatment of the differentiated thyroid cancers (papillary and follicular) is changing secondary to ongoing research, which is helping us tailor our therapeutic regimens. The extent of surgery varies and is based on a very through preoperative assessment, which often includes imaging studies to access for local and metastatic disease. The ultrasound of the soft tissue of the neck allows for a complete assessment of the cervical lymph nodes and is used to determine the extent of a lymph node dissection. After the surgery is completed, the need for radioactive I-131 should be considered to ablate any thyroid remnant that remains. Unlike the “old days,” not everyone requires treatment. Those who do should be treated only after a low-iodine diet and consideration for treatment with two injections of recombinant thyroid stimulating hormone to avoid withdrawal from the levothyroxine.
In contrast, external beam radiotherapy (EBRT) is used infrequently in differentiated thyroid cancer. The American Thyroid Association (ATA) guidelines suggest its use in patients over age 45 who have disease outside the thyroid at surgery and who have a high likelihood of tumor remaining at the microscopic level. It is also indicated in those patients with gross residual tumor who are deemed not to be candidates for further surgery or RAI.
Patients who now receive EBRT do so with advanced radiation techniques. Those who undergo irradiation of the head and neck region are at risk for long-term effects to the salivary glands and larynx. One modern technique called intensity modulated radiation therapy (IMRT) is able to spare more healthy tissue by dividing the beam into individual beamlets and varying the dose so that it is lowest adjacent to healthy tissues. These sophisticated radiation modalities offer better coverage of the target and less normal tissue sequelae, providing a favorable treatment option for highly selected patients.
Review of the individual cases by the endocrine (thyroid) tumor board allow for a multidisciplinary and personalized approach to treatment in accordance with national guidelines. The dosage and goals of thyroid suppressive therapy are determined based on the staging of the tumor and re-evaluated with time. Thyroid ultrasounds and thyroglobulin panels are monitored, looking for signs of re-occurrences and metastasis. Repeat nuclear medicine whole-body studies and stimulated thyroglobulin levels are sometimes utilized, depending on the patient’s clinical status. PET scans are only considered in situations in which the thyroglobulin levels are rising and are not taking up radioactive I-131. Patients with metastatic disease can be considered for innovative clinical trials.
The promise of optimizing integration of targeted therapies, which are currently being tested in clinical trials, means the future is bright. Phase II studies have already shown efficacy for agents such as axitinib, sorafenib and motesanib. Researchers are evaluating angiogenesis inhibitors, immunomodulators and even gene therapy. Thyroid specialists will thus have more options than ever before to diagnose these malignancies earlier with the promise of tailored, effective therapies.
Adapted from Florida MD, February 2013