Thyroid cancer epidemiology and prognostic variables

Thyroid cancer comprises a broad spectrum of diseases with variable prognoses. Although most patients with this disease have excellent overall survival, there are some who do not fare so well. With the worldwide increase in incidence, the need to identify which tumours pose the greatest risk to patients is more acute than ever. This paper will discuss this rising trend in incidence with an analysis of the possible reasons for the increase. In addition, the paper will explore the factors that portend a worse prognosis for the individual patient. Finally, the limitations of the current staging systems will be discussed, with particular emphasis on why they are not as informative in the management of patients with thyroid cancer.

A consensus report of the role of serum thyroglobulin as a monitoring method for low-risk patients with papillary thyroid carcinoma

Recent studies have provided new information regarding the optimal surveillance protocols for low-risk patients with differentiated thyroid cancer (DTC). This article summarizes the main issues brought out in a consensus conference of thyroid cancer specialists who analyzed and discussed this new data. There is growing recognition of the value of serum thyroglobulin (Tg) as part of routine surveillance. An undetectable serum Tg measured during thyroid hormone suppression of TSH (THST) is often misleading. Eight studies show that 21% of 784 patients who had no clinical evidence of tumor with baseline serum Tg levels usually below 1 micro g/liter during THST had, in response to recombinant human TSH (rhTSH), a rise in serum Tg to more than 2 micro g/liter. When this happened, 36% of the patients were found to have metastases (36% at distant sites) that were identified in 91% by an rhTSH-stimulated Tg above 2 micro g/liter. Diagnostic whole body scanning, after either rhTSH or thyroid hormone withdrawal, identified only 19% of the cases of metastases. Ten studies comprising 1599 patients demonstrate that a TSH-stimulated Tg test using a Tg cutoff of 2 micro g/liter (either after thyroid hormone withdrawal or 72 h after rhTSH) is sufficiently sensitive to be used as the principal test in the follow-up management of low-risk patients with DTC and that the routine use of diagnostic whole body scanning in follow-up should be discouraged. On the basis of the foregoing, we propose a surveillance guideline using TSH-stimulated Tg levels for patients who have undergone total or near-total thyroidectomy and (131)I ablation for DTC and have no clinical evidence of residual tumor with a serum Tg below 1 micro g/liter during THST.

Management of papillary and follicular (differentiated) thyroid cancer: new paradigms using recombinant human thyrotropin

The incidence of differentiated thyroid cancer (DTC) has increased in many places around the world over the past three decades, yet this has been associated with a significant decrease in DTC mortality rates in some countries. While the best 10-year DTC survival rates are about 90%, long-term relapse rates remain high, in the order of 20-40%, depending upon the patient's age and tumor stage at the time of initial treatment. About 80% of patients appear to be rendered disease-free by initial treatment, but the others have persistent tumor, sometimes found decades later. Optimal treatment for tumors that are likely to relapse or cause death is total thyroidectomy and ablation by iodine-131 ((131)I), followed by long-term levothyroxine suppression of thyrotropin (TSH). On the basis of regression modeling of 1510 patients without distant metastases at the time of initial treatment and including surgical and (131)I treatment, the likelihood of death from DTC is increased by several factors, including age >45 years, tumor size >1.0 cm, local tumor invasion or regional lymph-node metastases, follicular histology, and delay of treatment >12 months. Cancer mortality is favorably and independently affected by female sex, total or near-total thyroidectomy, (131)I treatment and levothyroxine suppression of TSH. Treatments with (131)I to ablate thyroid remnants and residual disease are independent prognostic variables favorably influencing distant tumor relapse and cancer death rates. Delay in treatment of persistent disease has a profound impact on outcome. Optimal long-term follow-up using serum thyroglobulin (Tg) measurements and diagnostic whole-body scans (DxWBS) require high concentrations of TSH, which until recently were possible to achieve only by withdrawing levothyroxine treatment, producing symptomatic hypothyroidism. New paradigms, however, provide alternative pathways to prepare patients for (131)I treatment and to optimize follow-up. Patients with undetectable or low Tg concentrations and persistent occult disease can now be identified within the first year after initial treatment by recombinant human (rh)TSH-stimulated serum Tg concentrations greater than 2 microg/l, without performing DxWBS. These new follow-up paradigms promptly identify patients with lung metastases that are not evident on routine imaging, but which respond to (131)I treatment. In addition, rhTSH can be given to prepare patients for (131)I remnant ablation or (131)I treatment for metastases, especially those who are unable to withstand hypothyroidism because of concurrent illness or advanced age, or whose hypothyroid TSH fails to increase.

Sodium iodide symporter in health and disease

Radioiodine-concentrating activity in thyroid tissues has allowed the use of radioiodine as a diagnostic and therapeutic agent for patients with thyroid disorders such as well-differentiated thyroid cancer. However, some extrathyroidal tissues also take up radioiodine, contributing to unwanted side effects of radioiodine therapy. Now that the molecule that mediates radioiodine uptake, the sodium iodide symporter (NIS), has been cloned and characterized, it may be possible to develop novel strategies to differentially modulate NIS expression and/or activity, enhancing it in target tissues and impeding it in others. In addition to restoring NIS expression/activity to ensure sufficient radioiodine uptake for the diagnosis and treatment of advanced thyroid cancers, we envision that it may be possible to selectively increase or confer NIS expression/activity in tumors of nonthyroidal tissues to facilitate the use of radioiodine in their diagnosis and treatment. We also consider the molecular basis of thyroid and nonthyroid disorders that may be complicated by NIS deregulation. Finally, we explore the use of NIS as an imaging reporter gene to monitor the expression profile of the transgene in transgenic mouse animal models and in patients undergoing gene therapy clinical trials.

Long-term outcome of patients with differentiated thyroid carcinoma: effect of therapy

OBJECTIVE

To present an overview of current therapeutic practices and results in patients with differentiated thyroid carcinoma.

METHODS

Personal series of patients and selected studies reported in the literature are reviewed relative to outcome (tumor recurrence and cancer-related mortality) after treatment of differentiated thyroid cancer.

RESULTS

In the United States, thyroid carcinoma ranks 14th in incidence among the major malignant tumors. Although many factors influence the long-term outcome with papillary and follicular thyroid carcinoma, the patient's age at the time of diagnosis, tumor stage, and initial treatment are the most important. The risk of death from thyroid cancer becomes substantially greater after age 40 years and increases dramatically after 60 years of age. Tumor recurrence is more prevalent before age 20 and after age 60 years. Delay in therapy for more than a year after initial manifestation also has been shown to have an adverse effect on outcome. The optimal initial treatment is usually near-total thyroidectomy and surgical excision of extrathyroidal tumor, when possible. For complete ablation of residual thyroid tissue, radioactive iodine therapy is usually necessary and should be followed by thyroid hormone suppression of serum thyrotropin concentrations. A schedule of 6-month follow-up intervals is recommended, until the serum thyroglobulin is undetectable and 131I whole-body scanning shows no uptake in the neck or extrathyroidal sites.

CONCLUSION

An aggressive approach to management of differentiated thyroid carcinoma is likely to render about 90% of patients permanently free of disease.

Using recombinant human TSH in the management of well-differentiated thyroid cancer: current strategies and future directions

Mortality rates from thyroid cancer have fallen significantly in recent decades, almost certainly as the result of earlier diagnosis and improved treatment of differentiated (papillary and follicular) thyroid cancer. Enhanced survival is likely a result of early diagnosis and therapy applied at a disease stage when treatment is most effective. In the United States and Europe, most patients at high risk for relapse and death from thyroid cancer are treated with total or near-total thyroidectomy and receive radioiodine ablation of residual normal or malignant thyroid tissue, followed by treatment with thyroid hormone, a strategy that cures more than 80% of patients. Still, some die of the disease and nearly 15% have local recurrences, while another 5% to 10% develop distant metastases. Over 50% of recurrences appear in the first five years, but distant metastases may surface years, and sometimes decades, after initial therapy. Much has been learned about risk stratification to predict recurrence and death from thyroid cancer but individual patients continue to have adverse outcomes not always foreseen by a low tumor stage. Follow-up must accordingly be meticulous and prolonged. The National Cancer Center Network (NCCN) has recently established consensus practice guidelines that give explicit advice about the diagnosis and management of benign and malignant thyroid tumors, including paradigms for long-term follow-up and the treatment of recurrent disease. The guidelines confirm that diagnostic scanning with 131I and measurement of serum thyroglobulin (Tg) levels are the mainstay of follow-up, offering the opportunity to detect recurrent or persistent cancer at very early stages. These guidelines advocate TSH-stimulated serum Tg measurements, done either during thyroid hormone withdrawal or stimulation with recombinant human TSH (rhTSH, Thyrogen), that often identify the presence of cancer well before diagnostic whole-body scanning or other imaging studies can spot the tumor, which offers the opportunity to treat recurrent disease at an early stage. The use of rhTSH adds a new dimension to long-term follow-up that avoids putting patients through the symptoms of hypothyroidism, and offers the opportunity to follow some patients with rhTSH-stimulated serum Tg levels without performing 131I whole-body scans. A multicenter international study has shown that serum Tg measurements alone are not as sensitive in the identification of patients with persistent or recurrent tumor as are rhTSH-stimulated serum Tg determinations. Although not yet approved for preparation of patients for 131I therapy, rhTSH has been used successfully in a compassionate use program for this purpose in a relatively large number of patients. Formal clinical investigations now planned to provide guidelines for the use of rhTSH for therapeutic 131I portend a new set of effective therapeutic paradigms for the management of differentiated thyroid cancer.

Hormonal regulation of radioiodide uptake activity and Na+/I- symporter expression in mammary glands

The observation that radioiodide uptake (RAIU) activity, mediated by the Na+/I- symporter (NIS), is significantly increased in lactating breast suggests that RAIU and NIS expression in mammary gland are modulated by hormones involved in active lactation. We showed that both the NIS expression level and RAIU in rat mammary gland are maximal during active lactation compared to those in the mammary glands of virgin and pregnant rats as well as the involuting mammary gland. In the lactating mammary gland, NIS is clustered on the basolateral membrane of alveolar cells as a lesser glycosylated form than NIS in thyroid. The RAIU of lactating mammary gland was partially inhibited by treatment with a selective oxytocin antagonist or bromocriptine, an inhibitor of PRL release. These findings suggest that RAIU and NIS expression in mammary gland are at least in part modulated by oxytocin and PRL. Indeed, we showed that NIS messenger ribonucleic acid level was increased in a dose-dependent manner by oxytocin and PRL in histocultured human breast tumors.

Hypothyroidism after treatment for nonthyroid head and neck cancer

OBJECTIVES

To determine the incidence of posttreatment hypothyroidism in patients treated with surgery with or without radiotherapy for advanced-stage nonthyroid head and neck cancer and to make recommendations for its detection.

DESIGN

A prospective study to assess the incidence and time frame of occurrence of hypothyroidism in patients by primary tumor site and treatment modality. Thyroid function tests were performed preoperatively, at the first postoperative visit, and then approximately every 6 months. Patients were followed up for up to 3 years.

SETTING

Arthur G. James Cancer Hospital and Research Institute, Columbus, Ohio.

PATIENTS

A total of 251 patients with nonthyroid head and neck cancer were originally enrolled; 198 patients with evaluable data were studied to determine the incidence of posttreatment hypothyroidism. Approximately 80% of the patients had advanced stage (III or IV) or recurrent cancer.

RESULTS

The overall incidence of posttreatment hypothyroidism was 15% in 198 patients followed up for a mean of approximately 12 months. Hypothyroidism developed in 12% of patients treated with nonlaryngeal surgery and radiotherapy. The group undergoing total laryngectomy (with thyroid lobectomy) and radiotherapy had a 61% incidence of hypothyroidism. The average time to detection of hypothyroidism was 8.2 months.

CONCLUSIONS

Approximately 15% of patients treated for advanced head and neck cancer with surgery and radiotherapy will develop hypothyroidism. Those treated with total laryngectomy and radiotherapy are at greatest risk.

A comparison of recombinant human thyrotropin and thyroid hormone withdrawal for the detection of thyroid remnant or cancer

Recombinant human TSH has been developed to facilitate monitoring for thyroid carcinoma recurrence or persistence without the attendant morbidity of hypothyroidism seen after thyroid hormone withdrawal. The objectives of this study were to compare the effect of administered recombinant human TSH with thyroid hormone withdrawal on the results of radioiodine whole body scanning (WBS) and serum thyroglobulin (Tg) levels. Two hundred and twenty-nine adult patients with differentiated thyroid cancer requiring radioiodine WBS were studied. Radioiodine WBS and serum Tg measurements were performed after administration of recombinant human TSH and again after thyroid hormone withdrawal in each patient. Radioiodine whole body scans were concordant between the recombinant TSH-stimulated and thyroid hormone withdrawal phases in 195 of 220 (89%) patients. Of the discordant scans, 8 (4%) had superior scans after recombinant human TSH administration, and 17 (8%) had superior scans after thyroid hormone withdrawal (P = 0.108). Based on a serum Tg level of 2 ng/mL or more, thyroid tissue or cancer was detected during thyroid hormone therapy in 22%, after recombinant human TSH stimulation in 52%, and after thyroid hormone withdrawal in 56% of patients with disease or tissue limited to the thyroid bed and in 80%, 100%, and 100% of patients, respectively, with metastatic disease. A combination of radioiodine WBS and serum Tg after recombinant human TSH stimulation detected thyroid tissue or cancer in 93% of patients with disease or tissue limited to the thyroid bed and 100% of patients with metastatic disease. In conclusion, recombinant human TSH administration is a safe and effective means of stimulating radioiodine uptake and serum Tg levels in patients undergoing evaluation for thyroid cancer persistence and recurrence.

Early cellular abnormalities induced by RET/PTC1 oncogene in thyroid-targeted transgenic mice

The RET/PTC1 oncogene, a rearranged form of the RET proto-oncogene, has been reported to be associated with human papillary thyroid carcinomas. We have shown that targeted expression of RET/PTC1 in the thyroid gland leads to the development of thyroid carcinomas in transgenic mice with histologic and cytologic similarities to human papillary thyroid carcinoma. To further investigate how RET/PTC1 expression contributes to the pathogenesis of papillary thyroid tumor, the time of tumor onset and the early phenotypic consequences of RET/PTC1 expression in thyrocytes were determined. All high copy transgenic mice developed bilateral thyroid tumors as early as 4 days of age. At embryological days 16-18, increased proliferation rate, distorted thyroid follicle formation and reduced radioiodide concentrating activity were identified in transgenic embryos. The reduced radioiodide concentrating activity was attributed to decreased expression of the sodium-iodide symporter. Our study showed that RET/PTC1 not only increased proliferation of thyrocytes, it also altered morphogenesis and differentiation. These findings provide a model for the role of RET/PTC1 in the formation of abnormal follicles with reduced iodide uptake ability observed in human papillary thyroid carcinoma.

Recognizing thyrotoxicosis

Clinical manifestations of thyrotoxicosis range from silent to florid and can mimic those of other conditions occurring in pregnancy and old age. The diagnosis may be particularly vexing in elderly patients with apparent dementia. Once clinical suspicion has been aroused, the workup to confirm the diagnosis and establish the cause is easily accomplished.

Regulation of monocyte survival in vitro by deposited IgG: role of macrophage colony-stimulating factor

IgG deposition at tissue sites characteristically leads to macrophage accumulation and organ injury. Although the mechanism by which deposited IgG induces tissue injury is not known, we have recently demonstrated that deposited IgG stimulates the release of IL-8 and monocyte chemoattractant protein-1 from normal human monocytes, which may drive inflammation. Since IgG also induces macrophage accumulation in these diseases, we hypothesized that deposited IgG protects monocytes from apoptosis. As an in vitro model of the effect of deposited IgG on monocyte survival, monocyte apoptosis was studied after FcgammaR cross-linking. Monocytes cultured on immobilized IgG, which induces FcgammaR cross-linking, were protected from apoptosis, whereas monocytes cultured with equivalent concentrations of F(ab')2 IgG or 50 times higher concentrations of soluble IgG, neither of which induces FcgammaR cross-linking, were not protected. Moreover, this protection was transferable, as supernatants from immobilized IgG-stimulated monocytes protected freshly isolated monocytes from apoptosis and contained functional M-CSF, a known monocyte survival factor. M-CSF mediated the monocyte survival induced by FcgammaR cross-linking, as neutralizing anti-human M-CSF Abs blocked the monocyte protection provided by either immobilized IgG or IgG-stimulated monocyte supernatants. These findings demonstrate a novel mechanism by which deposited IgG targets tissue macrophage accumulation through FcgammaR-mediated M-CSF release. This pathway may play an important role in promoting and potentiating IgG-mediated tissue injury.

An overview of the management of papillary and follicular thyroid carcinoma

Long-term survival rate for papillary and follicular carcinoma is more than 90%, but this varies considerably among subsets of patients. About 30% of patients, however, develop tumor recurrence, depending on the initial therapy. Two-thirds of the recurrences occur within the first decade after therapy, but the others may appear years later. We found that among patients with recurrent cancer, 30% could not be fully eradicated and another 15% died of disease. Tumor recurred outside the neck in 21% of our patients, most commonly in the lungs (63%), which resulted in death in about half the patients. Mortality rates are lower when recurrences are detected early by radioiodine scans rather than by clinical signs. We believe that the best treatment for most patients with differentiated thyroid carcinoma is near-total thyroidectomy followed by 131I ablation of the thyroid remnant, which in our experience reduces the recurrence rate, improves survival and facilitates follow-up. A long delay in initiating this therapy has an adverse and independent effect on prognosis, more than doubling the 30-year cancer mortality rate. If only partial lobectomy has been performed, it is best to consider completion thyroidectomy for lesions 1 cm or larger because of the high rate of residual carcinoma in the contralateral lobe. Completion thyroidectomy and 131I whole-body scanning allows for the diagnosis and treatment of unrecognized carcinoma and when performed early, results in significantly fewer lymph node and hematogenous recurrences and enhances survival. A large and growing number of studies demonstrates decreased recurrence of papillary carcinoma and decreased disease-specific mortality attributable to 131I therapy. On the basis of our observations and other studies, we believe that an aggressive approach to initial management and follow-up may render nearly 90% of the patients permanently free of disease. Periodic follow-up should be done with whole-body scanning and serum thyroglobulin (Tg) measurements, performed either during thyroid hormone withdrawal or by recombinant human thyrotropin (TSH)-stimulated scanning and Tg measurement. A scheme for follow-up management is presented.

Development of reverse transcription-competitive polymerase chain reaction method to quantitate the expression levels of human sodium iodide symporter

The sodium iodide symporter (NIS) is the plasma membrane protein that mediates active iodide uptake into thyroid follicular cells. To investigate whether human NIS (hNIS) mRNA levels in papillary thyroid carcinomas (PCs) correlate with the ability of tumors to concentrate radioiodide, we developed a reverse transcription-competitive polymerase chain reaction (RT-cPCR) method to quantify the hNIS mRNA levels in thyroid tissues. We studied 7 normal thyroid tissues, 8 PCs, and 1 follicular adenoma. hNIS mRNA levels in PCs were generally lower than those found in normal thyroid tissues. The reduced radioiodide concentrating activity of PCs is due, at least in part, to the reduced expression and/or the decreased stability of hNIS mRNA.

Recognizing the faces of hypothyroidism

Physicians may not recognize hypothyroidism if they rely on the stereotypical picture of the disorder. The age of the patient, stage of the disease, and other illnesses or conditions such as pregnancy can change the clinical presentation. The signs and symptoms of hypothyroidism are remarkably diverse. Instead of a single picture, physicians need a mental gallery.

Thyroid carcinomas in RET/PTC transgenic mice

The RET/PTC oncogene, a rearranged form of the RET proto-oncogene, has been found to be associated with human papillary thyroid carcinomas. To investigate whether RET/PTC causes papillary thyroid carcinoma, we generated a transgenic mouse model of papillary thyroid carcinoma with targeted expression of RET/PTC1 in the thyroid gland. Thyroid tumors in these RET/PTC1 transgenic mice are characterized by a slow growth rate, thyroid-stimulating hormone (TSH)-responsive tumor progression, and loss of radioiodide-concentrating activity despite continued expression of thyroglobulin (Tg). The time of tumor onset appears to be dependent on the expression level of RET/PTC1 in these transgenic mice. In high-copy RET/PTC1 transgenic mice, cellular abnormalities, including a slightly increased proliferation rate, aberrant follicle formation, and loss of radioiodide-concentrating activity, can be readily identified at embryological day 18. To identify which signaling pathway or pathways perturbed by RET/PTC1 are essential for RET/PTC1 to induce tumor development, we generated transgenic mice carrying a thyroid-targeted RET/PTC1 triple mutant, which contains tyrosine to phenylalanine mutations at tyrosine residues 294, 404, and 451. Initial characterization of the thyroid glands of these RET/PTC1 triple-mutant transgenic mice showed no change in follicular morphology or radioiodide-concentrating activity. This finding suggests that signaling pathways mediated by one or more of these three phosphotyrosine binding sites are essential for RET/PTC1 to induce thyroid tumor development. Finally, in order to investigate whether tumors induced by RET/PTC3 are more aggressive than those tumors induced by RET/PTC1, we also generated thyroid-targeted RET/PTC3 transgenic mice.

An immunohistochemical study of Na+/I- symporter in human thyroid tissues and salivary gland tissues

The human Na+/I- symporter (hNIS) is the plasma membrane protein that mediates active iodide uptake into several tissues, such as the thyroid and salivary glands. To study the distribution and cellular localization of the hNIS protein, we have generated a polyclonal antibody that could detect the hNIS protein by immunohistochemical staining on tissue sections. In normal thyroids, hNIS expression is heterogeneous, and it is only detected in sporadic thyrocytes of a given follicle. The hNIS protein was not detected in thyroid carcinomas, yet it was detected in the majority of thyrocytes in Graves' thyroids. In salivary glands, hNIS protein was not detected in acinar cells, but it was detected in ductal cells. The hNIS proteins are clustered in the basal and lateral membranes in cells stained positive for hNIS.

Thyroxine suppressive therapy in patients with nodular thyroid disease

PURPOSE

To review evidence about thyroxine suppressive therapy in patients with thyroid nodules, including the clinical importance and natural history of nodules and the effects and potential side effects of thyroxine therapy.

DATA SOURCES

English-language articles published from 1986 to December 1996 were identified through searches of the MEDLINE database, selected bibliographies, and personal files.

DATA EXTRACTION

Randomized, controlled trials and nonrandomized trials of thyroxine suppressive therapy for solitary and predominantly solid thyroid nodules were reviewed. In most studies, nodule cytology was evaluated by fine-needle aspiration biopsy. Therapy was considered suppressive if suppression was documented by thyroid-stimulating hormone-releasing hormone tests or sensitive thyroid-stimulating hormone assays. Response was defined as a decrease of 50% or more in nodule size or volume; most recent studies measured nodule size by ultrasonography.

DATA SYNTHESIS

The evidence suggests that thyroxine suppressive therapy fails to shrink most nodules: Only 10% to 20% of nodules responded to this treatment. Fine-needle aspiration biopsy is more reliable in distinguishing benign from malignant nodules. Recent studies suggest that spontaneous decrease in size with complete disappearance of thyroid nodules is not uncommon. No data show that thyroxine therapy arrests further growth in most existing nodules or prevents the emergence of new nodules. Postoperative thyroxine therapy does not seem to prevent recurrence of thyroid nodules except in patients with a history of radiation therapy. Potential adverse effects of long-term suppressive therapy include osteoporosis and heart disease.

CONCLUSIONS

Patients with cytologically benign nodules are best followed without thyroxine treatment. Most benign nodules remain stable in size and remain benign when monitored for a long time. For nodules that increase in size, biopsy should be done again or surgery should be performed.