Q&A: Thyroid cancer

Thyroid cancer is a disease in which cancer cells are found in the tissue of the thyroid gland.

Camilo Jimenez, M.D., assistant professor in Endocrine Neoplasia and Hormonal Disorders at MDAnderson, answers questions about this disease.

Are there several types of thyroid cancer?
Yes, there are four types of thyroid cancer. The most common is papillary thyroid cancer; the second is follicular thyroid cancer; the third, medullary thyroid cancer; and the rarest, anaplastic thyroid cancer.

In general, papillary thyroid cancer exhibits the best survival rate and prognosis with survival rates up to 100% after five years of initial diagnosis, even in patients with metastatic disease.

Anaplastic thyroid cancer is perhaps the most aggressive cancer that humans may suffer from. Almost 100% of patients survive fewer than three months after its diagnosis. Fortunately it is very rare.

How common is thyroid cancer?
Papillary thyroid cancer is very common. Its incidence has increased during the last decade, and now it's one of the 10 most common cancers in the United States.

What causes thyroid cancer?
In most papillary and follicular thyroid cancer cases, we do not know the cause.

Approximately 3% of papillary thyroid cancer cases have predisposition because other family members have been affected by this disease. Exposure to sublethal radiation, such as that observed in survivors of radiation from Hiroshima, Nagasaki or Chernobyl, is another risk factor for the disease.

In the case of medullary thyroid carcinoma, up to 35% of patients may have a genetic predisposition.

The causes of follicular and anaplastic thyroid carcinomas are unknown.

What are the symptoms of thyroid cancer?
These tumors are usually found because of the presence of a palpable or visible neck mass. Frequently, they're accidentally found by radiographic studies recommended to evaluate diseases that are not related to thyroid cancer.

In some cases, thyroid cancer is found because of manifestations related to metastatic disease (for example, a fracture due to skeletal metastases).

Papillary, follicular and anaplastic thyroid carcinomas usually do not secrete hormones. Medullary thyroid carcinomas secrete excessive amounts of calcitonin (a hormone produced in the thyroid) making some patients susceptible to flushing and chronic diarrhea.

What are the most common treatments?
Surgery is the most important treatment for thyroid cancer. In a vast majority of papillary and follicular thyroid carcinomas, once surgery is performed, ablation therapy with radioactive iodine is recommended.

Thyroid suppressive therapy with a dosage of thyroid hormone -- enough to suppress the thyroid-stimulating hormone -- is required after ablation therapy in almost every patient. For medullary thyroid cancer, ablation with radioactive iodine and thyroid suppressive therapy are not necessary.

What other information can you share?
We've noticed that both the incidence and aggressiveness of thyroid cancer have increased over the last decade. Some tumors present with metastases that are not possible to remove by surgery.

To attack these tumors, we now have drugs that target molecular pathways important for the tumor development and survival. Many of these drugs are under evaluation in clinical trials, and they include names such as sorafenib, sunitinib, motesanib, XL184, E7080 and others. A new era for thyroid cancer has begun.