Cystic well-differentiated squamous cell carcinoma of the thymus: a clinicopathological and immunohistochemical study of six cases

Aims: To present six cases of cystic well-differentiated squamous cell carcinoma of the thymus. Methods and results: The patients were six men aged between 48 and 75years (average: 61.5years) who were symptomatic with chest pain, shortness of breath, and dyspnoea. Diagnostic imaging showed anterior mediastinal masses, and surgical resection was accomplished in all cases. Grossly, the tumours measured 40-90mm in greatest diameter (average: 65mm), and were described as ill-defined lesions with a prominent cystic component and focal areas of haemorrhage and necrosis. Histologically, they were characterized predominantly by their cystic architecture. The cyst walls were lined by squamous epithelium showing different degrees of cellular atypia. In focal, more solid areas, the tumours showed evidence of keratinization. By immunohistochemistry, tumour cells were positive for cytokeratin 5/6, p40, and Pax8. All tumours were staged as T1N0M0 according to the Weissferdt-Moran staging system. Clinical follow-up showed that four patients have remained alive and well after a period ranging from 1 to 2years. Two patients were lost to follow-up. Conclusions: The current cases highlight an uncommon growth pattern of well-differentiated squamous cell carcinoma of the thymus that may cause diagnostic difficulty with mediastinoscopic biopsies.