Thyroid and Parathyroid Cancer

Thyroid cancer and parathyroid cancer are both malignant conditions affecting endocrine glands in the neck, but they are entirely distinct diseases. Despite their close anatomical location, they arise from different glands with separate functions, and they differ significantly in their causes, clinical features, and treatment approaches.

Hormones secreted by Thyroid and Parathyroid Glands

Thyroid Gland Hormones

• Thyroxine(T4) & Triiodothyronine (T3): Produced by follicle cells, these iodine-containing hormones regulate basal metabolic rate, energy, growth, and development.
• Calcitonin:  Secreted by parafollicular (C-cells), this hormone reduces calcium levels in the blood by inhibiting osteoclasts (bone-breaking cells)

Parathyroid Gland Hormones

• **Parathyroid Hormone(PTH):** Produced by chief cells, this hormone acts to increase blood calcium levels by stimulating calcium release from bones, increasing calcium absorption in the intestines, and reducing calcium excretion by the kidneys.

Hormonal Regulation

• Calcium Balance: Calcitonin and PTH work antagonistically to maintain calcium balance; calcitonin lowers blood calcium, while PTH raises it.
• Metabolism Control: T3 and T4 levels are controlled by Thyroid Stimulating Hormone (TSH) from the anterior pituitary.

Thyroid Cancer

Thyroid cancer is a malignancy that originates in the thyroid gland, a butterfly-shaped endocrine organ located at the base of the neck. The thyroid produces hormones that regulate metabolism, heart rate, and blood pressure. Thyroid cancer is relatively common, especially among women, and most forms are highly treatable when detected early.

Types

There are four main types of thyroid cancer:

• Papillary Thyroid Cancer: This is the most common type of thyroid cancer, accounting for approximately 80% of all cases. It is typically slow growing and often develops in a single lobe of the thyroid. Even when it spreads to nearby lymph nodes, it is usually highly treatable with excellent outcomes.
• Follicular Thyroid Cancer: This is the second most common type of thyroid cancer, accounting for about 10% of cases. It occurs more frequently in regions with low iodine intake. Unlike papillary thyroid cancer, it rarely spreads to lymph nodes but can metastasize to distant organs such as the lungs or bones.
• Medullary Thyroid Cancer (MTC): This type of thyroid cancer arises from the C cells of the thyroid gland, which produce the hormone calcitonin. It accounts for less than 5% of all thyroid cancers and is often more challenging to treat than other types. Medullary thyroid cancer may occur sporadically or as an inherited condition.
• Anaplastic Thyroid Cancer: This is the rarest and most aggressive form of thyroid cancer, accounting for less than 1% of all cases. It typically occurs in older adults and is characterized by extremely rapid growth and early spread. Anaplastic thyroid cancer often invades nearby structures such as the trachea, esophagus, and surrounding muscles, which can lead to symptoms like difficulty breathing, swallowing, or speaking.

Symptoms and Causes

Early-stage thyroid cancer often has no symptoms. The most common first sign is a lump or swelling in the neck, which may be painless. As the cancer progresses, other symptoms may include:

• A lump in the neck that can be felt through the skin.
• A change in voice, including increasing hoarseness.
• Difficulty swallowing.
• Pain in the neck and throat.
• Swollen lymph nodes in the neck.

While the exact causes are not fully understood, some risk factors include:

• Radiation exposure during childhood, such as from medical treatments.
• Family history of thyroid cancer or certain genetic syndromes.
• Gender: Women are more likely to be diagnosed with thyroid cancer than men.
• Age: It is often diagnosed in people between the ages of 20 and 55.

Treatment and Prognosis

Treatment for thyroid cancer typically involves surgery to remove all or a part of the thyroid gland (thyroidectomy). Other common treatments may include:

• Radioactive iodine (RAI) therapy: This is used to destroy any remaining thyroid cells, including cancer cells, after surgery.
• Thyroid hormone therapy: Patients who have their thyroid removed must take hormone replacement medication for life.
• Chemotherapy and targeted therapy: These are used for more advanced or aggressive types of thyroid cancer.

The prognosis for most types of thyroid cancer is excellent. The 5-year survival rate for localized thyroid cancer is nearly 100%, and the overall 5-year survival rate for all stages is over 98%. The prognosis for anaplastic thyroid cancer is poor due to its aggressive nature.

Parathyroid Cancer

Parathyroid cancer is an extremely rare disease in which malignant cells form in one of the four parathyroid glands. These pea-sized glands are located behind the thyroid gland and are responsible for producing parathyroid hormone (PTH), which regulates calcium levels in the blood and bones.

Types of Parathyroid Neoplasms & Conditions

• Parathyroid Carcinoma (Malignant): The primary cancer, often characterized by severe hypercalcemia and very high parathyroid hormone (PTH) levels.
• Atypical Parathyroid Adenoma: A tumor with some features of cancer (e.g., cellular atypia) but lacking clear evidence of invasion or metastasis.
• Parathyromatosis: A rare condition characterized by multiple small nodules of hyperfunctioning parathyroid tissue throughout the neck, often caused by rupture of a gland during previous surgery.
• **Parathyroid Adenoma(Benign):** The most common cause of primary hyperparathyroidism, which is not cancerous.
• Sporadic Carcinoma: Most cases arise randomly without known risk factors.

Symptoms and Causes

As parathyroid cancer is extremely rare, most doctors never encounter it in their practice. The most common signs and symptoms are caused by abnormally high levels of calcium (hypercalcemia) (>14mg/dL) and excessive production of parathyroid hormone (hyperparathyroidism) by the cancerous gland. These can include:

• Extreme fatigue and weakness.
• Bone pain and increased risk of fractures.
• Kidney stones.
• Frequent urination and excessive thirst.
• Nausea, vomiting, and loss of appetite.
• Lumps around the neck region

A small percentage of cases are linked to inherited genetic conditions. However, the exact cause for most cases is unknown.

Treatment and Prognosis

The primary treatment for parathyroid cancer is surgery to remove the affected gland along with any surrounding tissues that may be involved. This procedure, known as an en bloc resection, is essential for achieving a cure.

Unlike thyroid cancer, chemotherapy and radiation therapy are generally ineffective in treating parathyroid cancer. As a result, the prognosis depends largely on whether the tumor can be completely removed during surgery.

Overall, the prognosis for parathyroid cancer is less favorable than for thyroid cancer, mainly because it is often diagnosed at a more advanced stage. The five-year survival rate is approximately 85% across all stages. If the cancer recurs, it most commonly does so within a few years of the initial diagnosis.

Sources

Macmillan Cancer Support www.macmillan.org.uk Parathyroid cancer

MD Anderson Cancer Center www.mdanderson.org Thyroid Cancer

Mayo Clinic www.mayoclinic.org Thyroid cancer

FAQS

Thyroid Cancer FAQs

1. Is thyroid cancer common? Yes, thyroid cancer is one of the more common endocrine cancers, especially in women. However, the most frequent types are highly treatable with an excellent prognosis.

2. Is a lump in my neck always a sign of thyroid cancer? No. While a palpable lump or nodule in the neck is the most common symptom, over 95% of thyroid nodules are benign (non-cancerous).

3. Do blood tests detect thyroid cancer? No, there are no specific blood tests to directly diagnose thyroid cancer. However, doctors may check thyroid-stimulating hormone (TSH) levels to assess thyroid function. A diagnosis is typically made through a biopsy of a suspicious nodule.

4. Can thyroid cancer spread? Yes, while most types are slow-growing, thyroid cancer can spread (metastasize). It most commonly spreads to nearby lymph nodes in the neck. In more advanced cases, it can spread to distant organs like the lungs and bones.

5. What is the difference between papillary and follicular thyroid cancer? Papillary and follicular are both "differentiated" thyroid cancers, meaning their cells still look similar to normal thyroid cells. Papillary is the most common type and tends to spread to lymph nodes. Follicular is the second most common and is more likely to spread through the bloodstream to distant organs.

6. Will I need to take medication after my thyroid is removed? Yes. If you have a total thyroidectomy (removal of the entire thyroid gland), you will need to take a synthetic thyroid hormone replacement medication, typically for life. This replaces the hormones your body can no longer produce.

7. Can thyroid cancer return after treatment? Yes, there's a risk of recurrence even after successful treatment. This is why regular follow-up appointments, including blood tests and ultrasounds, are crucial to monitor for any signs of the cancer returning.

Parathyroid Cancer FAQs

8. How rare is parathyroid cancer? Parathyroid cancer is extremely rare. It's estimated to be diagnosed in fewer than 100 people in the United States each year.

9. What are the main symptoms of parathyroid cancer? Symptoms are primarily caused by high calcium levels in the blood (hypercalcemia), a condition resulting from the cancerous gland overproducing parathyroid hormone (PTH). Symptoms include extreme fatigue, bone pain, frequent urination, and kidney stones. A lump in the neck is also a common sign.

10. Why is parathyroid cancer difficult to diagnose? Parathyroid cancer is often difficult to diagnose because its symptoms are similar to those of the far more common benign (non-cancerous) parathyroid tumors. A definitive diagnosis is often only confirmed after the gland is surgically removed and examined.

11. Is surgery the only effective treatment for parathyroid cancer? Yes, surgery is the primary and most effective treatment. The goal is a complete surgical removal of the cancerous gland and any surrounding tissue that the cancer may have invaded. Unlike thyroid cancer, chemotherapy and traditional radiation are not typically effective.

12. What happens if I have high calcium levels due to parathyroid cancer? High calcium levels (hypercalcemia) are a serious complication. Your doctor will work to manage these levels with intravenous fluids and other medications before and after surgery to prevent severe health issues like kidney failure.

13. Does parathyroid cancer often come back? Yes. Parathyroid cancer has a high rate of recurrence, with more than half of cases returning, most commonly within 2 to 5 years after the initial surgery, which is why long-term follow-up care is essential.

General FAQs

14. Are these two cancers related? No. Although the thyroid and parathyroid glands are located next to each other in the neck, they are entirely separate glands with distinct functions. Thyroid cancer affects the thyroid gland, while parathyroid cancer arises in the parathyroid glands.

15. What are the different prognoses for these two cancers? The prognosis for thyroid cancer is generally excellent, particularly for the most common types, with a very high five-year survival rate. In contrast, parathyroid cancer has a less favorable prognosis because it is more aggressive and has a higher likelihood of recurrence. However, complete surgical removal of the cancerous gland can significantly improve the outcome.