Carcinosarcoma ex non-recurrent pleomorphic adenoma composed of TTF-1 positive large cell neuroendocrine carcinoma and myofibrosarcoma: apropos a rare Case.

We present a carcinosarcoma ex non-recurrent pleomorphic adenoma composed of a large cell neuroendocrine carcinomatous component and a spindle cell sarcoma with myofibroblastic differentiation. The tumor contained a hyalinized transition zone where the classical PA appeared to acquire two different histopathological patterns of malignant transformation of the epithelial component. The carcinomatous component was strongly and diffusely positive for low-molecular weight cytokeratins (AE1-3), synaptophysin, thyroid transcription factor-1 and focally positive for chromogranin A. All these markers were negative in the sarcomatous component. The sarcomatous component displayed immunoreactivity for smooth muscle actin with a predominantly linear, subplasmalemmal pattern. No expression of CD31, S100 protein, h-caldesmon, desmin, CD34, p63, myogenin, Myo D1 and c-kit was detected. Strong immunohistochemical expression of p53 was documented in both the carcinomatous and sarcomatous components as well as in the atypical epithelial component in the transition zone associated with the hyalinized pleomorphic adenoma.