The thyroid gland, located at the base of the neck, produces hormones that regulate metabolism. While most thyroid cancers originate from follicular cells, a distinct and much rarer form arises from immune cells within the tissue. This malignancy is known as thyroid lymphoma, a cancer that begins in lymphocytes (a type of white blood cell). It accounts for less than five percent of all thyroid malignancies. Timely diagnosis is important, as it often responds well to non-surgical treatments.
What Exactly is Thyroid Lymphoma
Thyroid lymphoma is a cancer of the lymphatic system that originates in the thyroid gland, classifying it as an extranodal lymphoma. It is almost exclusively classified as a B-cell Non-Hodgkin Lymphoma (NHL). Primary thyroid lymphoma starts in the thyroid, while secondary lymphoma is a spread from a tumor elsewhere in the body.
The two most common subtypes dictate the disease’s behavior and outlook. Diffuse large B-cell lymphoma (DLBCL) is the most frequent subtype (60 to 90 percent of cases), characterized by rapid growth and aggressive behavior. The second major type is Mucosa-Associated Lymphoid Tissue (MALT) lymphoma, an indolent, slow-growing cancer (10 to 30 percent of cases). MALT lymphoma can sometimes transform into the more aggressive DLBCL subtype over time.
Key Risk Factors and Causes
The development of primary thyroid lymphoma is strongly linked to Hashimoto’s thyroiditis, an autoimmune disorder causing chronic inflammation of the thyroid gland. This condition causes a long-term infiltration of lymphocytes into the thyroid, creating an environment of constant immune cell activity. This chronic proliferation of immune cells increases the risk for malignant transformation into lymphoma.
Individuals with Hashimoto’s thyroiditis have a risk of developing thyroid lymphoma up to 60 times higher than the general population. The process involves the long-term presence of B-cells, the source of most thyroid lymphomas, typically emerging decades after the initial autoimmune diagnosis. Most cases are diagnosed in older individuals, typically between 60 and 70 years of age, with a noticeable female predominance (women are affected three to four times more often than men).
How Doctors Identify Thyroid Lymphoma
Patients often present with a rapidly enlarging mass in the neck, a hallmark sign of thyroid lymphoma. This rapid growth can lead to compressive symptoms due to pressure on surrounding structures. These symptoms include difficulty swallowing (dysphagia), shortness of breath (dyspnea), or a change in voice. Some patients may also experience systemic symptoms, known as B-symptoms, including unexplained fever, night sweats, and unintentional weight loss.
The diagnostic process begins with a physical exam and imaging, such as an ultrasound, to visualize the thyroid and any enlarged lymph nodes. Computed tomography (CT) or Positron Emission Tomography (PET) scans are often used to determine the extent of the disease and check for spread. The most definitive step is obtaining a tissue sample through a biopsy.
While fine-needle aspiration (FNA) is commonly used for thyroid nodules, it often fails to provide enough tissue to accurately classify a lymphoma. Therefore, a core needle biopsy, which removes a larger sample, is frequently necessary to confirm the diagnosis. This biopsy determines the specific subtype (MALT or DLBCL) using specialized tests like flow cytometry and immunohistochemistry, which dictates the subsequent treatment plan.
Treatment Strategies
Treatment for thyroid lymphoma depends highly on the specific subtype and the stage of the disease. Unlike most other thyroid cancers, surgical removal of the gland is generally not the primary treatment. Lymphomas are systemic diseases that respond well to other therapies. Surgery is typically reserved for cases where the mass is causing acute airway obstruction or for obtaining a large tissue sample for diagnosis.
For the aggressive Diffuse Large B-cell Lymphoma (DLBCL), a multimodal approach is standard, combining chemotherapy with immunotherapy. This often utilizes the R-CHOP regimen (Rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone). This is frequently followed by radiation therapy to the neck area. In contrast, the indolent MALT lymphoma, especially when confined to the thyroid, may often be treated effectively with radiation therapy alone. The overall prognosis for primary thyroid lymphoma is generally positive, especially with early stage disease, due to its sensitivity to these systemic treatments.