Primary thyroid lymphoma (PTL) is a rare type of cancer. Also called primary lymphoma of the thyroid, PTL occurs when abnormal lymphocytes (a type of white blood cell) grow and build up in the thyroid. This organ, which is found at the base of the neck, makes hormones — molecules that control many processes in the body.

PTL is rare. Less than 5 percent of thyroid cancers and up to 2.5 percent of lymphomas are PTL, according to a study published in the Annals of Medicine and Surgery. Women are more likely than men to develop PTL. The condition usually develops in people who are 65 to 75 years old.

What Is Primary Thyroid Lymphoma?

Like other types of lymphoma, PTL develops in the cells that make up the lymphatic system, which is responsible for fighting infection, getting rid of waste, and removing extra fluid. Parts of the lymphatic system include:

• Lymphatic vessels, which transport waste and fluid
• Lymph nodes, which filter the fluid
• Various organs, including the thyroid, which have their own functions or help fight infection

The thymus contains several types of lymphocytes, which may cause PTL if they become cancerous. Other types of lymphoma can develop in other locations and then spread to the thyroid gland. This is known as secondary thyroid lymphoma. Knowing where the lymphoma began is important because primary and secondary thyroid lymphomas are treated differently and lead to different outcomes.

Types of Primary Thyroid Lymphoma

One thing all cases of PTL have in common is that they develop in cells within the thyroid. However, the thyroid contains many kinds of cells, from which different cancers arise. PTL can be divided into multiple types of lymphoma. According to the study, most cases are subtypes of non-Hodgkin lymphoma, including:

• Diffuse large B-cell lymphoma (DLBCL) — 50 percent to 80 percent of cases
• Mucosa-associated lymphoid tissue (MALT) lymphoma — 20 percent to 30 percent of cases
• Follicular lymphoma, small lymphocytic lymphoma, and Burkitt’s lymphoma — rare cases

Hodgkin lymphoma accounts for about 7 percent of PTL cases.

What Are the Risk Factors for Primary Thyroid Lymphoma?

People with Hashimoto’s thyroiditis are 40 to 80 times more likely to develop PTL, the authors of the Annals of Medicine and Surgery study wrote. Hashimoto’s thyroiditis is a condition in which the immune system attacks the thyroid, causing the organ to leak high levels of thyroid hormone into the blood. Although Hashimoto’s thyroiditis increases the risk of PTL, less than 1 percent of people with Hashimoto’s thyroiditis are eventually diagnosed with PTL.

Signs and Symptoms of Primary Thyroid Lymphoma

In people who have PTL, lymphocytes fill the thyroid gland, making it bigger. This may lead to a thyroid mass, which feels like an enlarged lump in the neck. A mass can press on the windpipe, leading to compressive symptoms such as:

• Dysphagia (trouble swallowing)
• Dyspnea (shortness of breath)
• Facial swelling
• Hoarseness

Most people with PTL have a thyroid that works normally. However, according to the study, 1 in 10 people with this condition have hypothyroidism, in which the gland doesn’t make enough hormones. Low levels of thyroid hormones may cause symptoms such as fatigue, weak or achy muscles, joint pain, sensitivity to cold, dry skin, weight gain, constipation, anemia, memory problems, and depression.

Sometimes people with PTL also experience B symptoms — weight loss, fever, and night sweats — which are also common in other types of lymphoma.

The symptoms of PTL can develop quickly. If you notice any of these symptoms come on suddenly, talk with your doctor right away.

Diagnosis of Primary Thyroid Lymphoma

Blood tests, imaging tests, biopsies, and laboratory tests can be used to diagnose PTL. These tests help detect cancer and determine whether it has spread.

Blood Tests

Doctors check thyroid function using blood tests. Measuring levels of thyroid-stimulating hormones can show if a person has hypothyroidism. However, blood tests don’t reveal what is causing thyroid problems or directly detect PTL.

Imaging Tests

Imaging tests such as ultrasound allow doctors to look inside the neck and see the thyroid gland and nearby lymph nodes.

Biopsy

During a biopsy, doctors take a small sample of tissue so that cells can be more closely studied. People with PTL may need biopsies of the thyroid and lymph nodes. Doctors often recommend a procedure called fine-needle aspiration (FNA) biopsy, in which a very thin needle is used to remove thyroid cells.

An FNA biopsy removes only a small amount of cells. To obtain a larger sample, doctors may perform a core needle biopsy, which involves a bigger needle and can remove more cells. Doctors may even need to perform surgery to remove a piece of the thyroid.

Laboratory Tests

Biopsy samples are further studied in the laboratory. Tests such as immunohistochemistry can help determine the type of cells found in the thyroid and whether these cells are cancerous.

Staging

If a person is diagnosed with PTL, doctors will run additional tests to determine the lymphoma stage. The cancer’s stage describes how advanced it is and how far it has spread. Doctors use tests like positron emission tomography scans to look for cancer cells in other parts of the body.

Treatment of Primary Thyroid Lymphoma

Treatment depends on the disease stage and the type of lymphoma found in the thyroid. Doctors generally use a combination of radiation therapy and chemotherapy to treat PTL. These treatments usually work quickly to kill cancer cells and prevent their spread.

Radiation Therapy

During radiation therapy, a machine delivers high-energy particles or beams to kill cancer cells.

People who have MALT lymphoma that is localized (has not spread) might receive radiation therapy alone. Radiotherapy keeps this condition under control for 70 percent to 100 percent of people, according to the study mentioned previously. For those who have other types of PTL or PTL that has begun to spread, doctors typically recommend a combination of radiation therapy and chemotherapy.

Chemotherapy

Doctors often give multiple chemotherapy drugs at the same time when treating PTL. One common chemotherapy regimen is called CHOP, which consists of cyclophosphamide (Cytoxan), doxorubicin (also known as hydroxydaunorubicin and sold as Adriamycin), vincristine sulfate (formerly sold as Oncovin), and prednisone.

Targeted Therapies

By recognizing and blocking specific molecules found on cancer cells, targeted therapies help kill cancer cells while leaving healthy cells alone. Doctors are increasingly prescribing targeted drugs to treat lymphoma. For example, rituximab (Rituxan) is often used to treat DLBCL. It may be added to chemotherapy, such as with the R-CHOP regimen mentioned above. Targeted therapies often help improve outcomes compared with traditional treatments.

Surgery

Some people with PTL have surgery to remove the thyroid tumor. However, many doctors do not recommend this treatment. Most cases of PTL respond very well to chemotherapy, and surgery often doesn’t improve the outlook. However, surgery may be beneficial for treating certain types of PTL, such as MALT lymphoma.

Doctors occasionally recommend surgery to help treat PTL symptoms, such as when the airway is blocked by a thyroid mass. This treatment can also lead to additional complications, however.

What Is the Outlook for Primary Thyroid Lymphoma?

A person’s outlook for PTL depends on the disease stage and lymphoma type. In one study, researchers measured how long people lived, on average, after receiving a PTL diagnosis. They found that survival rates varied by lymphoma stage:

• Stage 1 (cancer cells in thyroid gland only) — 9.3 years
• Stage 2 (spread to nearby lymph nodes) — 9 years
• Stage 3 (found in distant lymph nodes) — 8.1 years
• Stage 4 (spread to other parts of the body) — 7.5 years

Survival rates for PTL also depend on the type of lymphoma. The same researchers found that, among all lymphoma stages, people with DLBCL of the thyroid lived a mean of 8.5 years after being diagnosed. The mean survival rates for other subtypes were 9.2 years for Burkitt lymphoma, 10.2 years for follicular lymphoma, and 9.7 years for MALT lymphoma.

Besides advanced-stage cancer, factors that increase a person’s chances of having a poor outlook include:

• Large tumor size (more than 10 cm, or about four inches)
• A tumor that blocks the airway
• A tumor in the chest, in the space between the lungs
• High-grade (fast-growing) lymphoma cells
• High blood levels of lactate dehydrogenase or beta-2 microglobulin
• Older age (above 60 years)

If you are interested in learning more about your prognosis, talk with your health care team. Your doctors know your health history and tumor characteristics. They can help you better understand how these factors affect your outlook.

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