SAT570 Thyroid Lymphoma In A Patient With Hashimoto’s Thyroiditis

Disclosure: T. Aggarwal: None. S. Reyes: None. I.C. Glitza Oliva: None. E. Korytnaya: None. Background:Primary thyroid lymphoma (PTL) accounts for < 5% of thyroid malignancies. Patients with Hashimoto’s thyroiditis (HT) are at greater risk for developing PTL, with a relative risk of 67 compared to those without thyroiditis. The most common and more aggressive subtype of PTL is diffuse large B cell lymphoma (DLBCL) which is found in more than 50% of the cases, followed by MALT lymphoma and follicular lymphoma (FL), which represents only about 10% of cases. PTL can be classified as a nodular, diffuse, or mixed type based upon ultrasound (US) findings. Diffuse type PTL presents the biggest diagnostic challenge due to resemblance to thyroiditis on US imaging. Certain US features such as enhanced posterior echoes, markedly hypoechoic appearance of thyroid tissue and linear echogenic strands are suggestive of diffuse type PTL but can also be seen in HT. Positive predictive value for US was only 33.7% for diffuse type of PTL. Diagnosis of PTL is ultimately established by biopsy with immunophenotypic assessment. Management of PTL includes chemotherapy, radiation therapy or combined modality treatment. Given sensitivity of PTL to radiation and chemotherapy, surgery is rarely performed and is reserved only for alleviation of severe compressive symptoms in aggressive disease or protection of airway. Case Presentation: A 58-year-old female with 10-year history of HT, hypothyroidism and goiter underwent total thyroidectomy due to worsening compressive symptoms in her neck. She denied weight loss, fevers, or night sweats. Preoperative US showed enlarged heterogenous hypoechoic thyroid gland with echogenic strands and normal vascularity, consistent with the appearance in HT. Surgical pathology unexpectedly showed extensive follicular hyperplasia, focal grade 3b FL (80%), and large foci of DLBCL arising within FL (20%). Background changes of oncocyte metaplasia and lymphocytic infiltrates consistent with Hashimoto Thyroiditis were described. Both cytogenic FISH studies as well as immunohistochemistry failed to reveal MYC and BCL2 and/or BCL6 rearrangements. Positron emission tomography (PET) scan showed mild to moderately fluorodeoxyglucose- avid lymph nodes in the right superior mediastinal, right superior paratracheal and left neck region. The patient has completed 6 cycles of R-CHOP chemotherapy with complete response as evidenced by normal follow up PET imaging. Conclusion:PTL is a rare malignancy and less than 1% patients with Hashimoto’s thyroiditis develop thyroid lymphoma. Diffuse- type PTL should be included in the differential diagnosis while managing patients with HT who present with worsening compressive symptoms involving aerodigestive tract and rapid enlargement of goiter and have markedly hypoechoic thyroid gland with heterogenous internal echoes and posterior acoustic enhancement on US images. Presentation: Saturday, June 17, 2023