Mixed Small Cell Undifferentiated Squamous Cell Carcinoma of the Thymus – A Clinicopathologic Study of 10 Cases
Sunil Badve, Oscar Cano, Yesim Gokmen-Polar, Ken Kesler, Pat Loehrer, Sunil Badve. Indiana University School of Medicine, Indianapolis, IN
Background: Mixed small cell undifferentiated squamous cell carcinoma of the thymus was described as an entity by Snover et al in 1978. They reported three cases where the tumor was composed of sheets of undifferentiated cells within which were present nests of squamous cells exhibiting only a mild degree of atypia. The transition was relatively abrupt with one to two layers of cells with mixed morphology. More recently, an additional case of a tumor with this morphology has been reported. However, the entity remains poorly described.
Design: To better understand this rare disease, following IRB approval, we reviewed our database of over 600 cases of thymic tumors, including 120 thymic carcinomas, to identify cases with mixed undifferentiated and squamous carcinoma features. The presenting symptoms, morphological spectrum, and outcomes data of these patients are presented. All but two patients were referred from outside institutions and had limited number of slides available for review.
Results: Ten patients were identified, six male and four female; age at diagnosis ranged from 22 to 79. One patient had a history of prostate cancer. The patients predominantly presented with respiratory related symptoms or chest pain, although three patients presented only with systemic symptoms such as fatigue and weight loss. Three patients also had signs or symptoms of paraneoplastic syndromes. Most patients had advanced disease at presentation with four patients presenting with unresectable disease. The diagnosis was based on review of H&E slides (range 3–20 slides/patient). The squamous component in all cases was well differentiated with slight to minimal degree of atypia. The undifferentiated component varied in cell size and often contained large/intermediate cells. The stroma was fibroblastic in all but one case. All but one patients developed metastases or died within 3 years of diagnosis. The tumors had been previously diagnosed as poorly differentiated carcinoma (four), well differentiated carcinoma (two) and in one case each high-grade non–small cell carcinoma, large cell nonkeratinizing with focal squamous differentiation and squamous cell carcinoma. Neuroendocrine features had been reported in two cases.
Conclusions: Mixed small cell undifferentiated squamous carcinoma is an under-recognized subtype of thymic carcinoma associated with poor prognosis. Recognition of this rare subtype should provide for better management of the patients with this aggressive form of thymic carcinoma.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 289, Wednesday Morning