{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,12]],"date-time":"2026-08-12T05:28:01Z","timestamp":1786512481918,"version":"build-2736575974"},"reference-count":13,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,8,12]],"date-time":"2026-08-12T00:00:00Z","timestamp":1786492800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Oncol."],"abstract":"\n Background<\/jats:title>\n Primary squamous carcinoma of the thyroid is an exceptionally rare malignancy, and its coexistence with poorly differentiated thyroid carcinoma (PDTC) is exceedingly uncommon. The pathogenesis of thyroid squamous carcinomas remains controversial, particularly when associated with congenital epithelial remnants such as branchial cleft-like cysts or thymic\/ultimobranchial remnants. We report an unusual collision tumor composed of PDTC and intrathyroid thymic carcinoma (ITTC) arising in association with a longstanding cystic thyroid lesion.<\/jats:p>\n <\/jats:sec>\n \n Case presentation<\/jats:title>\n A 59-year-old man initially presented with a left thyroid lesion that was interpreted as a benign branchial cleft cyst on ultrasound-guided fine-needle aspiration. After being lost to follow-up for more than four years, he re-presented with progressive enlargement of the lesion. Repeat cytology and core biopsy demonstrated a poorly differentiated carcinoma with squamous differentiation. Cross-sectional imaging revealed local invasion, retrosternal extension, and multiple bilateral pulmonary nodules suspicious for metastatic\u00a0disease. Near total thyroidectomy was performed for symptomatic airway\u00a0compression. Histopathological examination demonstrated two morphologically and immunophenotypically distinct malignant components: PDTC with solid, trabecular, and insular architecture, necrosis, increased mitotic activity, angioinvasion, lymphatic invasion, perineural invasion, and extrathyroidal extension; and a squamous carcinoma arising in association with a benign squamous-lined cyst. Immunohistochemically, the PDTC component expressed thyroglobulin, TTF-1, and PAX8, whereas the squamous component was positive for CK5\/6, p63, and CD117 and negative for thyroid follicular markers, supporting ITTC.<\/jats:p>\n <\/jats:sec>\n \n Outcome<\/jats:title>\n The final diagnosis was a collision tumor composed of PDTC and ITTC arising in association with a branchial cleft-like cyst or other embryologic cystic remnant. Although pulmonary biopsy and systemic treatment were planned, the patient developed severe bronchopneumonia and died before further staging could be completed.<\/jats:p>\n <\/jats:sec>\n \n Conclusion<\/jats:title>\n This case illustrates an exceptionally rare collision tumor of the thyroid and highlights the diagnostic limitations of cytologic assessment in predominantly cystic lesions. It emphasizes the importance of repeat evaluation of enlarging cystic thyroid masses and comprehensive histopathological and immunohistochemical assessment for accurate diagnosis and appropriate clinical management.<\/jats:p>\n <\/jats:sec>","DOI":"10.3389\/fonc.2026.1900434","type":"journal-article","created":{"date-parts":[[2026,8,12]],"date-time":"2026-08-12T04:41:28Z","timestamp":1786509688000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Collision tumor of poorly differentiated thyroid carcinoma and intrathyroid thymic carcinoma arising in association with a branchial cleft-like cyst: a case report"],"prefix":"10.3389","volume":"16","author":[{"given":"Sayed Ali","family":"Almahari","sequence":"first","affiliation":[{"name":"Pathology Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jehad","family":"Hammad","sequence":"additional","affiliation":[{"name":"Ear, Nose and Larynx Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Khalid","family":"Khan","sequence":"additional","affiliation":[{"name":"Radiology Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haneen","family":"Alboosta","sequence":"additional","affiliation":[{"name":"Surgical Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Worood","family":"Husain","sequence":"additional","affiliation":[{"name":"Ear, Nose and Larynx Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jawaher","family":"Alansari","sequence":"additional","affiliation":[{"name":"Pathology Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yusuf","family":"Barhoom","sequence":"additional","affiliation":[{"name":"Surgical Department, Salmaniya Medical Complex, Government Hospitals","place":["Manama, Bahrain"]},{"name":"General Surgery, Hepatobiliary and Transplantation Surgery, King Abdullah Medical City","place":["Manama, Bahrain"]},{"name":"Lecturer, Arabian Gulf University","place":["Manama, Bahrain"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,8,12]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1177\/0194599817698436","article-title":"Primary squamous cell carcinoma of the thyroid: A population-based analysis","volume":"157","author":"Au","year":"2017","journal-title":"Otolaryngol Head Neck Surg"},{"key":"B2","doi-asserted-by":"publisher","first-page":"47","DOI":"10.21037\/acr-23-192","article-title":"The coexistence of papillary thyroid carcinoma, anaplastic thyroid carcinoma (squamous cell carcinoma subtype) and poorly differentiated thyroid carcinoma: a case report","volume":"8","author":"Zhang","year":"2024","journal-title":"AME Case Rep"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.3389\/fsurg.2023.1205287","article-title":"Primary or metastatic branchial cleft carcinoma?: a case report","volume":"10","author":"Ma","year":"2023","journal-title":"Front Surg"},{"key":"B4","doi-asserted-by":"publisher","DOI":"10.3389\/fendo.2023.1273472","article-title":"Progress in diagnosing and treating thyroid squamous cell carcinoma under the 5th edition of WHO classification","volume":"14","author":"Ding","year":"2024","journal-title":"Front Endocrinol (Lausanne)"},{"key":"B5","doi-asserted-by":"publisher","DOI":"10.1053\/j.semdp.2020.03.003","article-title":"Poorly differentiated thyroid carcinoma","volume":"37","author":"Xu","year":"2020","journal-title":"Semin Diagn Pathol"},{"key":"B6","doi-asserted-by":"publisher","DOI":"10.1515\/biol-2022-0475","article-title":"Primary and metastatic squamous cell carcinoma of the thyroid gland: Two case reports","volume":"17","author":"Zhao","year":"2022","journal-title":"Open Life Sci"},{"key":"B7","doi-asserted-by":"publisher","first-page":"210","DOI":"10.1186\/s13000-015-0441-7","article-title":"Differential diagnostic value of CD5 and CD117 expression in thoracic tumors: a large scale study of 1465 non-small cell lung cancer cases","volume":"10","author":"Riegsmann","year":"2015","journal-title":"Diagn Pathol"},{"key":"B8","doi-asserted-by":"publisher","first-page":"45","DOI":"10.1016\/j.path.2022.09.006","article-title":"No longer well-differentiated: Diagnostic criteria and clinical importance of poorly differentiated\/high-grade thyroid carcinoma","volume":"16","author":"Cracolici","year":"2023","journal-title":"Surg Pathol Clin"},{"key":"B9","doi-asserted-by":"publisher","DOI":"10.71152\/ajms.v15i11.4228","article-title":"Poorly differentiated and undifferentiated (anaplastic) carcinoma of thyroid with diagnostic challenges: A case series","volume":"15","author":"Shit","year":"2024","journal-title":"Asian J Med Sci"},{"key":"B10","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMra1501993","article-title":"Biologic and clinical perspectives on thyroid cancer","volume":"375","author":"Fagin","year":"2016","journal-title":"N Engl J Med"},{"key":"B11","doi-asserted-by":"publisher","DOI":"10.1001\/jama.2023.26348","article-title":"Thyroid cancer: a review","volume":"331","author":"Boucai","year":"2024","journal-title":"JAMA"},{"key":"B12","volume-title":"Nccn Guidelines\u00ae: Thyroid Carcinoma. Version 2.2026","year":"2026"},{"key":"B13","doi-asserted-by":"publisher","DOI":"10.1089\/thy.2020.0944","article-title":"2021 American Thyroid Association guidelines for management of patients with anaplastic thyroid cancer","volume":"31","author":"Bible","year":"2021","journal-title":"Thyroid"}],"container-title":["Frontiers in Oncology"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fonc.2026.1900434\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,12]],"date-time":"2026-08-12T04:41:42Z","timestamp":1786509702000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fonc.2026.1900434\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,12]]},"references-count":13,"alternative-id":["10.3389\/fonc.2026.1900434"],"URL":"https:\/\/doi.org\/10.3389\/fonc.2026.1900434","relation":{},"ISSN":["2234-943X"],"issn-type":[{"value":"2234-943X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,12]]},"article-number":"1900434"}}