PSAT295 Low Grade B-CELL Lymphoma and Follicular Cancer in a Patient with Hashimoto's Thyroiditis Presenting as Two Different Thyroid Nodules

We present an 88 year old female with a history of hypothyroidism due to Hashimoto's thyroiditis who noted a lump in the left side of her neck. Thyroid ultrasound revealed multiple nodules throughout the thyroid gland. The right lobe contained a 4.3 cm solid, dominant nodule and the left lobe contained a 4.2 cm lobulated hyperechoic nodule. Ultrasound-guided fine-needle aspiration biopsy of the 4.3 cm right thyroid nodule revealed follicular lesion of undetermined significance with predominantly Hurthle cells. Thyroseq was positive for aTERT and EIF1AX mutations. Ultrasound-guided fine-needle aspiration biopsy of the 4.2 cm left thyroid nodule revealed malignant cells consistent with a low-grade B-cell lymphoma. She underwent a total thyroidectomy. The final pathology report revealed both a 5.5 cm follicular carcinoma in the right lobe and a low-grade B-cell lymphoma most compatible with extra nodal marginal zone lymphoma of the mucosa associated lymphoid tissue (MALT lymphoma) involving predominantly the left lobe of the thyroid. She is beginning radiation treatment for the lymphoma. Three months after radiation treatment is completed, she will undergo radioactive iodine treatment for the follicular carcinoma. Thyroid cancer is the most common endocrine malignancy. However, the thyroid is an uncommon site of cancer overall, accounting for only 1.5% to 4.7% of new cancer cases in the general population of the United States. Malignant lymphoma presenting as a primary neoplasm in the thyroid is even more uncommon and represents only 1 to 5% of all thyroid malignancies. Hashimoto's thyroiditis is a known risk factor for MALT lymphoma. However, there is no known association between Hashimoto's thyroiditis and follicular carcinoma. There are several reports of patients with presence of both papillary thyroid cancer and MALT lymphoma. One case was reported of simultaneous MALT lymphoma and medullary thyroid cancer. This is the first case of a patient with both follicular thyroid cancer and MALT lymphoma in the thyroid gland. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.