Shadow cell differentiation in tumours of the colon and uterus.

We report on six patients with tumours of visceral organs (three patients with endometrial adenocarcinoma with squamous cell differentiation, one patient with atypical hyperplasia of endometrium, and two patients with adenocarcinoma of the colon with squamous cell differentiation), where unquestionable differentiation into shadow cells was observed. In all six cases the shadow cells were found mostly in the morules of immature squamous cells. The shadow cells were morphologically identical, on the light microscopical and ultrastructural level, to similar cells found in pilomatricomas. They were often accompanied by granulomatous giant cell reaction and calcification.