Practice Essentials
Primary thyroid lymphoma can be defined as a lymphoma that arises from the thyroid gland. [1] This definition excludes those that invade the thyroid gland as a consequence of either metastasis or direct extension. Primary thyroid lymphomas are practically always non-Hodgkin lymphomas (NHLs). Primary thyroid Hodgkin lymphoma is extremely rare. It represents less than 5% of thyroid malignancies.
NHLs can be divided into aggressive and indolent cell types. The most common subtype of NHLs that arise primarily from the thyroid gland is diffuse large-cell lymphoma (DLBCL).
Thyroid NHL represents approximately 1.2 to 1.7% of all NHLs. [2] It is highly curable, without the need for extensive surgery. Accordingly, early recognition and correct treatment of this condition is vital. it is most commonly a B-cell lymphoma. Mucosa-associated lymphoid tissue (MALT) lymphoma (MALToma) is another subtype that can arise from the thyroid gland and usually has a more favorable outcome than DLBCL.The best treatment results for primary thyroid large-cell lymphoma are with combined-modality therapy; for primary thyroid MALToma, radiation therapy alone is probably adequate. [3, 4]
Pathophysiology
Thyroid lymphomas are very frequently associated with Hashimoto thyroiditis. [5] Indeed, Hashimoto thyroiditis is an identified risk factor for primary thyroid lymphoma; patients with Hashimoto thyroiditis have a 60 times higher risk of developing primary thyroid lymphoma, compared with the general population. The hypothesis is that chronic antigenic stimulation secondary to the autoimmune disorder leads to chronic proliferation of lymphoid tissue, which eventually undergoes a mutation that leads to the development of lymphoma.
It has also been reported that a mutation or deletion in A20, which is a negative regulator of NF-кB signaling pathway, plays a role in the pathogenesis of certain subsets of thyroid B-cell lymphoma, especially MALTomas. [6]
Epidemiology
Primary thyroid lymphoma is rare. Estimates vary; primary thyroid lymphoma may constitute 1–8% of all thyroid malignancies and 1-7% of all extranodal lymphomas. [7, 8, 9] The incidence has been steadily increasing, with an annual change of 3.2%. [10]
As with other non-Hodgkin lymphomas, the median age of presentation in patients with thyroid lymphoma is approximately 60 years. [11, 8] Patients are rarely younger than 40 years. Most cases occur in women; the female-to-male ratio is 3-4:1.
Prognosis
The prognosis for patients with thyroid large-cell lymphoma usually is favorable because they typically present with localized disease, which is amenable to treatment with chemotherapy and radiation (see Treatment). A cohort study of 2215 patients with primary thyroid lymphoma from the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute reported 5- and 10-year overall survival rates of 71.61% and 55.95%, respectively. The 5- and 10-year lymphoma-specific survival rates were 85.7% and 82.2%, respectively. [10]
A study of 69 patients with primary thyroid lymphoma that evaluated prognostic factors found that the following were adverse factors for survival [12] :
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Age > 70 years
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Elevated LDH level
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Advanced clinical stage
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Aggressive histologic subtype
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High Ki-67 score
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Ultrasound elastography score > 3
A rare case of pulmonary metastasis has been reported in a 65-year-old woman diagnosed with a primary thyroid MALToma who underwent total thyroidectomy, followed by chemotherapy. After 5 years of follow-up, she was diagnosed with metastatic thyroid MALT lymphoma. [12]
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Rapidly enlarging thyroid mass occurring in association with neck adenopathy.
