Primary thyroid lymphoma

Pitfalls in the staging of cancer of thyroid

Thyroid cancer includes several neoplasms originating from the thyroid gland-from indolent and curable histologies of differentiated thyroid carcinoma to aggressive anaplastic thyroid carcinoma. Differentiation of thyroid nodules is problematic on CT and MR imaging unless there is evidence of extrathyroidal extension. Evaluation of regional lymph nodes is often performed clinically or with ultrasound. The retropharyngeal and mediastinal lymph nodes are better evaluated by CT and MR imaging. Nuclear scintigraphy is useful for staging and treatment of distant metastasis in differentiated thyroid carcinoma. PET may have a role in aggressive cancers. Accurate staging affects surgical management and subsequent therapy.

Thyroid carcinoma-associated genetic mutations also occur in thyroid lymphomas

Molecular testing for mutations activating the mitogen-associated protein kinase signaling pathway is being used to help diagnose thyroid carcinomas. However, the prevalence of these mutations in thyroid lymphomas has not been reported. Therefore, we studied the prevalence of BRAF, NRAS, HRAS, and KRAS mutations in 33 thyroid lymphomas and correlated the mutational status with the clinical, pathological, cytogenetic, and immunophenotypic findings. Eleven cases were also tested for PAX8/PPARγ translocations. The lymphomas included 25 diffuse large B-cell lymphomas, 6 extranodal marginal-zone lymphomas of mucosa-associated lymphoid tissue type, and 2 follicular lymphomas. Seventeen diffuse large B-cell lymphomas were germinal center type, six non-germinal center type, and two unclassifiable (Hans algorithm). None of the cases had an associated thyroid carcinoma. Mutations of the BRAF gene were identified in six (24%) diffuse large B-cell lymphomas (D594G in three germinal center diffuse large B-cell lymphomas, K601N in two germinal center diffuse large B-cell lymphomas, and V600E in one non-germinal center diffuse large B-cell lymphoma) and of the NRAS gene in two (8%) non-germinal center diffuse large B-cell lymphomas (Q61K and Q61H). BRAF and NRAS mutations were not found in any extranodal marginal-zone lymphomas of mucosa-associated lymphoid tissue type or follicular lymphomas. HRAS and KRAS mutations were not identified in any of the cases, nor were PAX8/PPARγ translocations found. Thus, interpretation of finding a BRAF or NRAS mutation in the thyroid, particularly in preoperative thyroid aspirates, must take into account the differential diagnosis of a lymphoma. In addition to the diagnostic importance, our data also demonstrate that alteration in the mitogen-associated protein kinase pathway may have a role in the pathogenesis of some large B-cell lymphomas of the thyroid with potential therapeutic implications.

PET and PET/CT in the management of thyroid cancer

The introduction of PET(-CT) has brought about a major paradigm shift in the management of thyroid carcinoma, especially from the diagnostic standpoint. From the viewpoint of patient management, the areas where it has made significant impact include the following: (1) the detection of disease focus in patients with differentiated thyroid carcinoma with elevated Tg levels and negative radioiodine scan. When localized disease is identified with F-18 FDG-PET-CT, surgery or focused radiotherapy could be utilized to eradicate the tumor; (2) the localization of disease in patients of MTC with elevated serum calcitonin levels; (3) the detection of unsuspected focal F-18 FDG uptake in the thyroid in patients undergoing whole body F-18 FDG PET for a different indication. This would prompt a workup to rule out thyroid carcinoma. The use of I-124 is evolving at this time and has been of great promise with regard to (a) its better efficacy of lesion detection and (b) the ability to provide lesion-specific dosimetry. In addition, F-18 FDG PET appears to be of potential value in patients with thyroid lymphoma in making the initial diagnosis, monitoring therapeutic response, and assessing for residual disease and/or recurrence.

Anaplastic thyroid cancer and primary thyroid lymphoma: a review of these rare thyroid malignancies

BACKGROUND

To review the current literature on the treatment of anaplastic thyroid cancer (ATC) and thyroid lymphoma (TL).

RESULTS

Both anaplastic carcinoma (ATC) and TL represent rare forms of thyroid cancer. ATC behaves in a highly aggressive manner, resulting in significant morbidity and mortality. Multimodality therapy consisting of both radiotherapy (RT) and chemotherapy is essential in obtaining local/regional control. Although ATC has been relatively chemo resistant, newer agents such like taxotere show promise. The role of surgery in the treatment of ATC continues to evolve, presently it should be reserved for patients who have shown an initial response to multimodality therapy and in patients in whom a complete macroscopic resection can be achieved with minimal morbidity. The successful treatment of TL currently lies in accurately diagnosing the histological subtype. Both large B-cell and mixed lymphomas are best treated with multimodality therapy consisting of CHOP combined with hyper-fractioned RT. MALT lymphomas with there more indolent course may be amenable to single modality RT or total thyroidectomy if diagnosed at an early stage IE.

DISCUSSION

Although both ATC and TL are rare, it is important for surgeons to be aware of the need for multimodality therapy when treating these patients and to understand the limited role surgery plays in diagnosis and treatment.

Maltoma of the thyroid and Sjögren's syndrome in a woman with Hashimoto's thyroiditis

We report the case of a 70-yr-old woman with maltoma of the thyroid, Sjögren's syndrome, and a history of Hashimoto's thyroiditis. The patient underwent a total thyroidectomy for a recently growing mass of the thyroid, while being treated with L-thyroxine for Hashimoto's thyroiditis. Postoperatively, routine histologic examination was consistent with the diagnosis of chronic lymphocytic thyroiditis of autoimmune etiology. Three years later, the patient presented with high temperature, anorexia, and coughing. This time, a microscopic examination of deeper thyroid tissue sections and an immunohistochemical study revealed a low-grade, non-Hodgkin lymphoma, MALT type. Simultaneously, the diagnosis of Sjögren's syndrome was established and the patient is currently under investigation for generalized lymphoma. This case clearly demonstrates the difficulty in differentially diagnosing Hashimoto's thyroiditis from low-grade MALT lymphoma by the use of routine histologic examination.

Primary thyroid lymphomas

Primary thyroid lymphoma is a rare disease that continues to produce diagnostic and therapeutic dilemmas. There was great difficulty in distinguishing thyroid lymphoma from anaplastic thyroid carcinoma but, because of new immunocytochemical staining techniques and increased cytopathologic knowledge, our ability to diagnose thyroid lymphoma has improved drastically over the past decade. Surgery that was once the mainstay of treatment for this disease, now plays a minimal role. Current treatment regimens for primary thyroid lymphoma consist of chemotherapy (cyclophosphamide, doxorubicin, vincristine, and prednisone) and external beam radiation. The overall and distant relapse rates have been shown to be significantly lower in those patients receiving combined modality therapy compared to chemotherapy or radiation alone. Although the role of surgery has changed over time, it continues to play an important role, especially in confirming diagnoses through open biopsies, potentially providing local control in the more indolent subtypes, and may play a role in the palliation of symptoms for large obstructive lymphomas. The evolving classification of extranodal lymphomas has brought about a better understanding of the biologic behavior of these tumors. Most thyroid lymphomas are B-cell origin, with six different histologic subtypes, but there appears to be two distinct clinical and prognostic groupings of these rare tumors. The more indolent lymphomas are the subgroup of mucosa-associated lymphoid tissue (MALT) lymphomas comprising approximately 6% to 27% of thyroid lymphomas. This subgroup, when localized to the thyroid (stage IE), responds well to total thyroidectomy or radiation with a complete response rate of more than 90%, leading some authors to recommend surgery as primary therapy in the treatment of localized MALT lymphomas. Therefore, surgery as a primary treatment for thyroid lymphomas would only be recommended under ideal conditions, such as MALT subtype stage IE only, and completely resectable with minimal morbidity. Unfortunately, this scenario is rarely the case. The more common subtype, comprising up to 70% of cases, is diffuse large B-cell lymphoma. This subtype appears to have the most aggressive clinical course with almost 60% of these tumors diagnosed with disseminated disease. Up to 40% of all diffuse large cell lymphomas appear to have undergone transformation from a MALT lymphoma, but they behave in a similar fashion to diffuse large cell lymphomas. Treatment for these tumors should include chemotherapy and radiation. The overall 5-year survival for this aggressive group is less then 50%. Surgery is rarely beneficial in diffuse large cell lymphoma and the mixed large cell subtypes because the disease is generally disseminated and surgical excision of all disease is not possible or associated with increased morbidity. However, there may be a role for palliative surgical debulking to alleviate obstructive symptoms while the patient is undergoing standard chemotherapy and radiation.