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MON-343 Thyroid Nodule Evaluation Resulting in a Diagnosis of Medullary Thyroid Cancer and Papillary Thyroid Carcinoma Collision Tumor: A Case Report

Year: 2025
Type: article
Study design: Case Report
Abstract: Disclosure: R. Heinrich: None. K. Kaput: None. Background: This case provides valuable teaching points by describing the extremely rare (<1% of all thyroid tumors) presentation of a collision tumor consisting of two histologically distinct forms of thyroid cancer, medullary thyroid cancer and papillary thyroid carcinoma. Preoperative imaging often fails to identify two morphologically different nodules and fine needle aspiration of the nodule often only identifies one type of cancer, as occurred in this case. With each tumor typically having a different stage and prognosis, management often requires consideration of each tumor individually. Case Description: A 37 year old female presenting with a thyroid nodule located in the isthmus, with associated lymphadenopathy, was subsequently found to have a collision tumor consisting of papillary thyroid carcinoma and metastatic medullary thyroid cancer. The patient was initially found to have a thyroid nodule at the age of 22. At the age of 37, a neck ultrasound revealed a thyroid nodule located in the isthmus measuring 17 mm described as solid, hypoechoic with irregular margins. This was associated with an abnormal appearing right lateral neck (level 3) lymph node which notably had an abnormal short-to-long axis ratio and central calcification. Ultrasound-guided fine needle aspiration of the isthmus nodule revealed papillary thyroid carcinoma while the lymph node aspirate was nondiagnostic and negative for thyroglobulin wash. Repeat biopsy of the level three lymph node showed findings consistent with malignancy, favoring medullary thyroid cancer, though there were insufficient cells for diagnosis. Calcitonin and CEA were elevated at 219 pg/mL (reference 0-5 pg/mL) and 4.8 ng/mL (ULN 4.7 ng/mL) respectively. The patient underwent total thyroidectomy, central neck dissection and right lateral neck dissection. Surgical pathology revealed papillary thyroid carcinoma (15 mm, classic subtype) as well as a focus of medullary thyroid cancer (9 mm), both located in the right thyroid lobe and isthmus with disruption of the capsule. Four out of nine lymph nodes in the right central neck, five out of nine in the right lateral neck and one out of fifteen in the left lateral neck were positive for medullary thyroid cancer. The medullary thyroid cancer was staged as PT1aPN1b and the papillary thyroid carcinoma was staged as P1Tb PN0a. The patient had no known family history of multiple endocrine neoplasia syndrome or medullary thyroid cancer. Conclusion: Thyroid collision tumors are often undiagnosed on neck ultrasound and fine needle aspiration and thus the diagnosis may not become apparent until pathology from a surgical resection of a seemingly single thyroid nodule confirms the presence of two distinct tumors. This case provides an example of how collision tumors may not be detected by standard thyroid nodule evaluations but can drastically change how a thyroid nodule is eventually managed. Presentation: Monday, July 14, 2025
Institution: University of Utah
Language: English
Field: Medicine
Open Access status: gold
Estimated APC paid: $3,255
OpenAlex ID: W4415451536
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