This left panel shows a histologic section taken through the full thickness of the esophageal wall.  Carcinomas of the esophagus are typically deeply infiltrating lesions and this one has extended through the muscularis propria (arrows).

The right panel shows nests of malignant squamous cells within the submucosa.  This is a moderately differentiated squamous cell carcinoma which shows keratin production.  The malignant cells show a common feature of malignancy, namely altered polarity.  The differentiating squamous cells within the submucosal nests cannot slough keratin to the luminal surface.  Instead, the keratin accumulates in the center of the nests as spherical keratin "pearls" (arrow).