Cancer of the Endocrine System
Summary of Key Points
Thyroid Cancer
Classification
• Differentiated thyroid cancer (DTC) includes papillary thyroid cancer (PTC), which accounts for 80% of all thyroid cancers, follicular thyroid cancer (FTC), which accounts for 10% to 20% of all thyroid cancers, and a rare type, Hürthle cell cancer.
• Medullary thyroid cancer (MTC) arises from the parafollicular C cells and accounts for 5% to 10% of all thyroid cancers.
• Anaplastic thyroid cancer is a rare, but rapidly fatal, form of thyroid cancer.
• Other histologic types of cancer, such as lymphoma, sarcoma, and metastatic cancers, can also be found within the thyroid.
Etiology
• Known risk factors for the development of thyroid cancer include radiation exposure and iodine deficiency.
• Thyroid cancer can also run in families or exist as part of familial syndromes (Gardner, Cowden, and Werner syndromes)
• More recently, the molecular pathogenesis of thyroid cancer has been investigated. The following are the most widely studied molecular markers for DTC to date:
• Well-differentiated histology has excellent 5-year survival (>95%).
• Older age and extent of invasion are related to prognosis.
• Lymph node involvement is associated with higher recurrence, but has questionable impact on survival.
• Many staging systems exist for DTC.
• Hürthle cell adenoma—larger size (>6 cm) predicts malignancy.
• Poorly differentiated tumors—recurrence lymph node metastases are common.
• Anaplastic cancers are extremely aggressive with 5-year survival less than 5%.
Presentation and Diagnosis
• The history should include radiation exposure, family history, and compressive symptoms (dysphagia, hoarseness, pain/pressure) from enlarging tumor.
• Concerning exam findings, include a fixed mass or lymphadenopathy.
• Incidental fining on computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and ultrasound.
• Preoperative laboratory studies include thyroid-stimulating hormone (TSH), Tg.
• Fine-needle aspiration (FNA) biopsy is a key component of the workup of thyroid nodules. The Bethesda Criteria classify FNA results and determine the risk of cancer in the nodule.
• Preoperative imaging should cervical ultrasound. CT is used when aggressive variants are suspected to assist in operative planning.
Treatment
• Treatment begins with surgery. Most thyroid cancers are treated with total thyroidectomy. Compartment-oriented neck dissection is added when there is metastatic disease in the cervical lymph nodes.
• Adjuvant therapy for differentiated tumors is radioactive iodine (131I).
• Patients must be prepared for radioactive iodine ablation with a low iodine diet.
• And thyroid hormone withdrawal or recombinant human thyroid-stimulating hormone (rhTSH) if there is no evidence of metastatic disease.
• After surgery and radioactive iodine, thyroxine-suppression prevents the growth of microscopic disease.
• External beam radiation is utilized for persistent, recurrent, anaplastic, poorly differentiated tumors that are not iodine avid.
• Chemotherapy is mainly palliative for poorly differentiated or anaplastic tumors. Traditional chemotherapy has minimal response rates, but newer, targeted therapies, such as sorafenib or sunitinib, are showing promise.
Recurrence
• Surveillance for recurrent thyroid cancer includes measurements of TSH, Tg, and antithyroglobulin antibodies in addition to cervical ultrasound. The schedule of these tests is tailored to risk level.
• Treatment of recurrence can include external beam radiation or targeted therapies, depending on the iodine avidity of the tumor.
Medullary Thyroid Cancer
• Medullary thyroid cancer accounts for 5% to 10% of all thyroid cancers; 75% of cases are sporadic and 25% are familial (multiple endocrine neoplasia [MEN]-2, familial medullary thyroid carcinoma [FMTC]).
• The diagnosis is made by FNA with calcitonin washout. RET testing can identify inherited germline mutations. As in DTC, cervical ultrasound assists with operative planning. The tumor markers calcitonin and carcinoembryonic antigen (CEA) can be useful in following patients postoperatively for identifying recurrence and metastases.
• At a minimum, treatment of MTC should consist of total thyroidectomy plus central lymph node dissection. Lateral neck dissection is added when there are clinically positive nodes in the central neck and for high-risk patients.
• Traditional chemotherapy is not effective for metastatic MTC, but newer, targeted therapies for metastatic disease such as vandetanib, have shown some promise.
Adrenocortical Cancer
• The incidence of adrenocortical cancer is 1 to 2 per million people.
• Most adrenocortical cancers are sporadic, but they can also occur as part of familial syndromes such as MEN-1, Li-Fraumeni syndrome, Beckwith-Wiedemann syndrome, and Carney complex.
• Most are asymptomatic, but 40% to 60% are functional (hormone production), and this may be the presenting symptom(s).
• The diagnosis is by urinary/plasma biochemical testing and imaging: CT, fluorodeoxyglucose (FDG)-PET.
• Often, the diagnosis is not made definitively until after resection of suspicious masses, and pathology provides definitive diagnosis. FNA of adrenal masses is rarely indicated.
• Surgery is the mainstay of treatment for adrenocortical cancer and should consist of en bloc resection of the adrenal gland with adjacent organs/tissue that is involved; cardiopulmonary bypass may be necessary for caval involvement.
• Long-term surveillance, consisting of physical exams and CT scans, is necessary to monitor for disease recurrence.
• Mitotane alone or in combination with other chemotherapeutic agents improves recurrence-free survival.
• Radiotherapy may improve local control, but there are no clear recommendations.
• Hormonal control can also limit disease spread and consists of mitotane, ketoconazole, metyrapone, etomidate.
• Excision or reoperation is recommended for recurrent or metastatic disease.
• The prognosis is poor, with overall 5-year survival of less than 40%.
Malignant Pheochromocytoma
• The incidence of malignant pheochromocytoma is 2 to 8 per 1,000,000 adults.
• Most malignant pheochromocytomas are sporadic, but 10% are part of inherited syndromes such as MEN syndromes, neurofibromatosis type I, von Hippel-Lindau syndrome, and succinate dehydrogenase gene mutations.
• Pheochromocytomas present with the classic triad of functional tumors-headache, tachycardia, and sweating, but they are asymptomatic in more than 50%, presenting as an incidental adrenal mass.
