[p40 Negative Basaloid Squamous Cell Carcinoma of the Lung;Report of a Case].

Immunohistochemical staining is important for the differential diagnosis of basaloid squamous cell carcinoma(BSC)and other similar carcinomas, such as small-cell carcinomas and large-cell neuroendocrine carcinomas. p40 is a useful marker of squamous cell carcinoma that can be used for the diagnosis of BSC. We present the case of a 64-year-old man who was referred to our hospital for investigation of an abnormal shadow revealed on chest radiography. Computed tomography(CT) revealed a 16×11 mm nodule in the left lung(S1+2), and a thoracoscopic left upper lobectomy was performed. Histologically, lobular pattern with peripheral palisading was observed and the immunohistochemical staining revealed the tumor cells to be positive for p63 and negative for both p40 and neuroendocrine markers, leading to the diagnosis of BSC.