Original ArticlesDesmoplastic Adamantinoma-like Thymic Carcinoma Clinicopathologic, Immunohistochemical, and Molecular Study of 5 CasesSuster, David I. MD*; Mejbel, Haider MD†; Mackinnon, Alexander C. MD, PhD†; Suster, Saul MD‡ Author Information *Department of Pathology, Rutgers University New Jersey Medical School, Newark, NJ †Department of Pathology, University of Alabama at Birmingham, Birmingham, AL ‡Department of Pathology, Medical College of Wisconsin, Milwaukee, WI Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: David I. Suster, MD, Department of Pathology, Rutgers University New Jersey Medical School, 150 Bergen Street, E142 Newark, NJ 07103 (e-mail: [email protected]). Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's website, www.ajsp.com. The American Journal of Surgical Pathology: December 2022 - Volume 46 - Issue 12 - p 1722-1731 doi: 10.1097/PAS.0000000000001947 Buy SDC Metrics Abstract Five cases of a heretofore unreported rare variant of thymic carcinoma characterized by a striking resemblance to adamantinoma of the mandible are described. The tumors occurred in 4 women and 1 man aged 58 to 76 years (mean: 67.8 y); they arose in the anterior mediastinum and measured from 5.3 to 12.0 cm in greatest diameter (mean: 8.9 cm). Presenting symptoms included chest pain, shortness of breath, and in 2 patients, pleural effusion. One tumor was asymptomatic and discovered incidentally. Histologically, the tumors were extensively desmoplastic, and the cellular proliferation was characterized by multiple islands of squamous epithelium with striking peripheral palisading of nuclei and central areas containing clear cells resembling a stellate reticulum. Areas of preexisting spindle cell thymoma were identified in 2 cases; these areas gradually merged with the higher-grade component of the lesion. Cystic changes were noted in 3 cases. Immunohistochemical studies in 3 cases showed the tumor cells were positive for cytokeratins, p40 and p63, and all showed a high proliferation rate (>50% nuclear positivity) with Ki-67. Next-generation sequencing was performed in 2 cases that showed amplification of the AKT1 gene (copy numbers 6 and 13). Clinical follow-up in 3 patients showed recurrence and metastasis after 1 and 2 years; 1 patient passed away 2 years after diagnosis due to the tumor. Desmoplastic adamantinoma-like thymic carcinoma represents an unusual histologic variant of thymic carcinoma that needs to be distinguished from metastases from similar tumors to the mediastinum. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.