Follicular thyroid cancer

Disease Description (Causes and Symptoms)

• Definition summary: Follicular thyroid cancer is a cancer belonging to the differentiated thyroid cancers and is a tumor originating from thyroid follicles (follicular cells). Along with papillary thyroid cancer, it is classified as differentiated thyroid cancer.
• Pathophysiology summary: Follicular cancer is diagnosed as malignant only when capsular invasion or vascular invasion is confirmed histologically. Whereas papillary cancer tends to metastasize through the lymph nodes, follicular cancer often metastasizes through the bloodstream to the bones, lungs, and other sites, and frequently absorbs radioactive iodine. Abnormalities in the regulation of cell growth and differentiation (genetic and environmental factors) are causes of its development.
• Main causes (associated factors): History of head and neck radiation exposure, family history, long-term low-iodine diet (regional differences), and other genetic predispositions.
• Main symptoms: Most cases are asymptomatic in the early stages and are often detected as nodules during health screenings. When symptoms occur, they may include a lump in the neck (nodule), difficulty swallowing, a foreign-body sensation in the throat, difficulty breathing, and voice changes (when the vocal cords are involved).
• Diagnostic features: Ultrasonography and fine-needle aspiration (FNA) are important for initial diagnosis, but because it is difficult to distinguish benign from malignant follicular lesions based only on cell morphology, postoperative histopathological examination (to confirm capsular and vascular invasion) is necessary for a definitive diagnosis.

Treatment Methods

• Surgery
  • Depending on the tumor size, extent of invasion, and clinical risk, a partial resection (lobectomy) or total resection (total thyroidectomy) is performed.
  • If lymph node metastasis is suspected, concomitant resection (lymph node dissection) may be performed.
• Radioactive iodine (RAI) therapy
  • Oral radioactive iodine is administered after surgery to remove residual thyroid tissue or microscopic metastatic lesions. It is often effective because follicular cancer frequently has a high rate of iodine uptake.
  • Before treatment, iodine uptake is increased through a low-iodine diet and elevation of TSH (by stopping thyroid hormones or administering rhTSH). Temporary isolation and precautions are required after treatment for radiation safety.
• Thyroid hormone medication (levothyroxine)
  • Taken as lifelong replacement therapy after thyroidectomy. It is also used to suppress TSH and reduce the risk of recurrence and growth (the intensity of treatment is adjusted according to risk).
  • Taking it on an empty stomach (in the morning) is recommended; it should be taken with a time interval from calcium, iron supplements, and similar products.
• Radiation therapy and systemic treatment
  • External beam radiation therapy (for local control) may be considered for locally advanced or metastatic lesions that cannot be controlled with surgery or RAI.
  • Molecular targeted therapies (e.g., tyrosine kinase inhibitors) may be used for extensive metastases or progressive lesions that do not absorb RAI (consultation with a specialist is required).
• Follow-up and tests
  • Long-term follow-up is conducted using blood thyroglobulin (Tg) and anti-Tg antibodies, thyroid ultrasonography, and, when necessary, whole-body imaging (radioactive iodine whole-body scans, PET/CT, etc.).
• Precautions, risk of complications, and self-management
  • Surgical complications: Hypoparathyroidism (hypocalcemia), recurrent laryngeal nerve injury (voice changes), bleeding, infection, and others.
  • RAI side effects: Temporary sialadenitis, dry mouth, and, rarely, effects on reproductive function (fertility)—women of childbearing age must avoid pregnancy before and after treatment and consult about pregnancy planning.
  • Medication interactions involving lifelong thyroid hormone use (calcium, iron, antacids, etc.) and the need to follow the dosing schedule carefully.
• Prognosis
  • Overall, it is considered a cancer with a good prognosis. Although outcomes vary depending on the stage and presence or absence of metastasis, long-term survival rates are high with appropriate surgery and RAI therapy.

Checklist Before an Outpatient Visit (Items to Bring, Records, and Tests)

• Items/documents to bring
  • A list of all medications currently being taken, including supplements and herbs
  • Previous thyroid ultrasound and FNA (cytology) results, and surgical and pathology records, if available
  • Recent blood test results (TSH, free T4, Tg, anti-Tg antibodies, etc.) and imaging test results (PET/CT, radioactive iodine scans, etc.)
• Symptom records
  • Changes in the size of the neck lump (when it began and whether it grew rapidly), difficulty swallowing, difficulty breathing, voice changes, and whether pain is present
  • Weight changes, fatigue, heat intolerance, sweating, and other symptoms related to thyroid function
• Lifestyle and medical history
  • History of head and neck radiation exposure, family history (thyroid cancer and endocrine diseases), pregnancy status (women of childbearing age), smoking, and alcohol use
• Preparation for tests
  • If radioactive iodine therapy is scheduled: Instructions on following a low-iodine diet, pregnancy testing (women), and confirmation of whether thyroid hormones should be stopped or whether rhTSH is planned
  • Regarding medication use: Patients taking thyroid hormones should be instructed to follow the guidance to “have blood drawn first, then take the medication” when undergoing blood tests.

Examples of General Questions to Ask the Doctor

• “What is the basis for diagnosing this lesion as malignant (follicular cancer) based on the pathology findings? (For example, whether capsular invasion or vascular invasion is present.)”
• “In my case, what is the appropriate extent of surgery (lobectomy vs. total thyroidectomy), and why?”
• “Is radioactive iodine therapy necessary after surgery? What are the expected effects and side effects?”
• “What target TSH level should be maintained with hormone therapy (levothyroxine)? What are the side effects?”

Examples of Disease-Specific Questions

• “Was capsular invasion or vascular invasion confirmed in the pathology results? (This information is decisive for determining the extent of surgery and the follow-up plan.)”
• “What is the schedule for Tg (thyroglobulin) testing and imaging to check for residual tissue or metastasis after surgery? What is the plan if Tg levels rise?”