Understanding Differentiated Thyroid Cancer

Doctors can classify thyroid cancers based on how cancer cells look under a microscope.

• Differentiated thyroid cancer (DTC): The cancer cells look similar to normal thyroid cells. DTCs account for the vast majority (more than 90%) of thyroid cancers. Types include papillary, follicular, and Hürthle cell thyroid cancers.
• Undifferentiated thyroid cancer (UTC): The cancer cells don’t look like normal thyroid cells. UTC typically refers to anaplastic thyroid cancer. Another type, medullary thyroid cancer, is also undifferentiated, but doctors usually consider it as a distinct type. Both are rare and more challenging to treat.
• Poorly differentiated thyroid cancer (PDTC): PDTC has features that are somewhere between DTC and UTC. PDTCs account for about 3% to 5% of all thyroid cancers. Doctors sometimes use this category to describe some Hürthle cell or medullary thyroid cancers.

Your thyroid contains two primary cell types. Follicular cells produce and secrete hormones. Parafollicular cells (aka C cells) specifically secrete calcitonin, which helps regulate calcium levels.

DTCs and anaplastic thyroid cancers originate in follicular cells, while medullary thyroid cancers originate in C cells.

DTCs that originate in the thyroid’s follicular cells include:

Papillary thyroid cancer

Papillary thyroid cancer is the most common type of thyroid cancer. About 80% to 85% of all thyroid cancers are papillary cancers.

Papillary thyroid cancer generally has a better outlook than follicular cancer. It usually grows very slowly but can spread to lymph nodes in the neck.

Follicular thyroid cancer

Follicular thyroid cancer is less common, accounting for 10% to 15% of all thyroid cancers. It also tends to grow slowly but can spread through the blood to distant organs like the lungs and bones.

There may be a link between follicular thyroid cancer and iodine deficiency.

Hürthle cell thyroid cancer

Hürthle cell thyroid cancer accounts for about 3% of thyroid cancers. Like other DTCs, these cancers start in the follicular cells. Historically, doctors considered them a subtype of follicular thyroid cancer.

However, Hürthle cells are larger and more distinct than other follicular cells, which is why doctors may consider them PDTCs. They’re also more difficult to detect and treat than other follicular thyroid cancers.

DTC usually doesn’t cause any symptoms except swelling in the neck. The swelling usually isn’t painful.

Some people with DTC may experience:

• hoarseness
• difficulty swallowing
• neck, jaw, or ear pain

You or a doctor may notice swelling or a lump (nodule) in your neck. A doctor may also find the nodule during an imaging test done for unrelated reasons.

A doctor might perform additional tests to check for signs of cancer, including ultrasound imaging and a thyroid nodule biopsy.

During a biopsy, a doctor inserts a thin needle into the thyroid nodule to remove a small amount of tissue and fluids. This type of biopsy is called fine-needle aspiration. The doctor will then send the sample to a laboratory for analysis under a microscope. Only a small number of nodules result in a cancer diagnosis.

Thyroid function tests aren’t usually helpful in diagnosing DTC.

Treatment for DTC depends on the size of the cancer. Since DTC is often small and grows slowly, doctors sometimes choose to wait before treating it. This is referred to as active surveillance or watchful waiting.

During this period of active surveillance, you will have an ultrasound every 6 to 12 months. Your doctor will look for any changes in the size of the tumor.

If the tumor grows or your doctor thinks there’s a high risk of it spreading to other organs, they may recommend surgery. Surgery could involve partial (lobectomy) or full removal of the thyroid gland (thyroidectomy) and, possibly, nearby lymph nodes.

As with all surgeries, thyroid removal surgery has risks and side effects. It’s important to discuss the risks and benefits of surgery for DTC with your doctor. You may decide that the benefits outweigh the risks and choose to have surgery earlier rather than wait to see if the tumor grows.

After a thyroidectomy, you will have to take thyroid hormone replacement therapy for the rest of your life.

Other treatments you may receive before or after surgery include:

• radioactive iodine therapy
• external radiation therapy
• chemotherapy
• targeted therapy

In most cases, DTC has a favorable outlook and is curable with surgery. Of the two types, follicular cancer may be slightly more aggressive than papillary cancer, but both types are highly treatable.

Your overall outlook will depend on your age, the size of the tumor, and if the cancer has spread (metastasized) to other parts of the body. Survival rates are highest for people younger than 55 years of age.

According to the American Cancer Society, 5-year relative survival rates for thyroid cancer that hasn’t spread outside the thyroid (localized), has spread to nearby organs (regional), or has spread to distant organs (distant) are as follows:

DTC is a slow-growing thyroid cancer. It’s the most common type of thyroid cancer and is highly treatable with surgery. The 5-year survival rate is above 98% if doctors detect and treat the cancer before it spreads to distant parts of the body.

Though most thyroid nodules aren’t cancer, speak with a doctor if you notice any unusual swelling or lumps in your neck.