Thyroid Cancer — NZ Condition Guide | KiwiMeds

What is Thyroid Cancer?

Thyroid cancer is cancer of the thyroid gland, located in the front of the neck. It is one of the more treatable cancers — most thyroid cancers are caught at an early stage and have excellent survival rates. The incidence of thyroid cancer has increased significantly in NZ over recent decades, partly due to more sensitive ultrasound scanning detecting small cancers. Around 600–700 new cases are diagnosed in NZ per year.

Overview

The most common types are papillary thyroid cancer (around 80% of cases — generally the most treatable, excellent prognosis), follicular thyroid cancer (around 10% — also generally good prognosis), medullary thyroid cancer (rare, may be inherited), and anaplastic thyroid cancer (rare but very aggressive). Most thyroid cancers present as a lump or nodule in the neck. Other symptoms can include hoarseness, difficulty swallowing, swollen lymph nodes in the neck, and neck pain. Many thyroid nodules are non-cancerous — ultrasound and fine needle aspiration (FNA) biopsy are used to assess them.

Treatment in New Zealand

Treatment depends on the type and stage. Most thyroid cancers are treated with surgical removal of the thyroid gland (thyroidectomy — total or partial). Radioactive iodine (RAI) is used after surgery for papillary and follicular cancers to destroy any remaining thyroid tissue. Thyroid hormone replacement (levothyroxine) is needed after total thyroidectomy — it also suppresses TSH, which can stimulate thyroid cancer cell growth. Targeted therapies are available for advanced thyroid cancers.

NZ-Specific Information

Thyroid surgery is performed by specialist surgeons at major NZ hospitals. The Thyroid Cancer Support Group NZ provides peer support. Endocrine NZ and the New Zealand Association of Endocrinologists provide specialist guidance. Levothyroxine is fully funded by Pharmac.

Frequently Asked Questions

Is thyroid cancer curable? For most types — particularly papillary and follicular thyroid cancer — the 10-year survival rate is over 90%. Will I need to be on medication after thyroid surgery? Yes — after total thyroidectomy, lifelong levothyroxine replacement is needed. Does thyroid cancer affect the immune system? The thyroid gland is not part of the immune system. Treatment with radioactive iodine requires brief isolation due to radiation safety.

Supplements That May Support Management

⚠️ Important: The supplements listed below have varying levels of clinical evidence. They are not a substitute for prescribed medications and should only be considered as adjunctive support under the guidance of a qualified healthcare professional. Always inform your GP or pharmacist before commencing any supplement, as interactions with prescribed medicines are possible.

• Selenium — Selenium is essential for selenoproteins including glutathione peroxidase and thioredoxin reductase, which protect thyroid cells from oxidative damage. Adequate selenium status supports thyroid health. Supplementation at 100–200 mcg/day is appropriate where deficiency is confirmed, but high-dose selenium is potentially harmful.
• Vitamin D — Vitamin D deficiency is associated with increased thyroid cancer risk and worse outcomes. Supplementation where deficiency is confirmed is appropriate and supports immune surveillance of residual thyroid tissue.
• CAUTION: Iodine supplements — Iodine supplementation or high iodine intake should ONLY be undertaken with explicit thyroidologist guidance in thyroid cancer management, as iodine requirements vary dramatically depending on treatment status (radioiodine therapy, remnant ablation, suppressive levothyroxine therapy).
• Calcium and Vitamin D (post-thyroidectomy) — Total thyroidectomy can damage the parathyroid glands, causing hypoparathyroidism and hypocalcaemia. Post-operative calcium and vitamin D supplementation may be required — this is a medical necessity guided by your endocrinologist.

Relevant Vaccinations

Individuals living with thyroid cancer may benefit from the following vaccinations. Please discuss your vaccination status with your GP or practice nurse, as eligibility and funding through the New Zealand National Immunisation Schedule may apply.

• Influenza (annual) — Recommended for all people with a history of cancer, particularly those on TSH-suppressive levothyroxine therapy which can affect immune function.
• COVID-19 — Maintaining COVID-19 vaccination is recommended for all thyroid cancer patients.
• Pneumococcal — Recommended for those on immunosuppressive treatments.

Dietary Guidance

Evidence-based dietary modifications play a meaningful role in the management of thyroid cancer. The following foods are generally recommended as part of a balanced, condition-appropriate diet. A referral to a registered dietitian may be beneficial for personalised nutritional planning.

• Selenium-rich foods (brazil nuts — 2 daily, seafood) — Brazil nuts are the most concentrated dietary selenium source. Two brazil nuts per day provides approximately the RDI of selenium (55–70 mcg), supporting thyroid protective antioxidant enzyme systems.
• Cruciferous vegetables (moderation on levothyroxine) — Raw cruciferous vegetables (broccoli, cabbage, kale) contain goitrogens that can marginally reduce thyroid hormone synthesis. In people with total thyroidectomy on levothyroxine replacement, this is not clinically significant — these vegetables can be eaten normally. Concerns apply primarily to those with functioning thyroid tissue.
• Iodine-containing foods (seafood, dairy) — consistency — Consistent iodine intake supports stable levothyroxine dosing. Sudden large changes in iodine intake (such as iodine-rich kelp supplements or contrast dyes before scans) can interfere with radioiodine therapy and thyroid function monitoring.
• Balanced nutrition for energy and immunity — Anti-cancer dietary patterns emphasising vegetables, fruits, whole grains, and lean protein support general immune function and recovery.

Related Conditions & Medications

Related medications: Levothyroxine. Related conditions: Hypothyroidism.