Immunohistochemistry of desmin and vimentin in smooth muscle tumors of the digestive tract.

The expression of desmin and vimentin in 35 "smooth muscle tumors" of the digestive tract was investigated using formalin-fixed and paraffin-embedded materials and the indirect immunoperoxidase method. Fourteen of 15 esophageal tumors and two of 15 gastric tumors were categorized as benign leiomyoma with low cellularity, and immunohistochemically were desmin-positive and vimentin-negative as were normal muscle layers of the digestive tract. The remaining tumors showed moderate to high cellularity: Six tumors seemed to be malignant on the basis of frequent mitosis and/or nuclear atypia, while 11 were considered to be of borderline malignancy. This cellular tumor group exhibited consistent vimentin immunoreactivity, but desmin was negative or only weakly and/or focally positive. S-100 protein was fundamentally negative in these tumors. The pitfalls of studying desmin immunohistochemistry as a routine diagnostic tool in surgical pathology are discussed.