Figure 1

Subepithelial myofibroblasts in pure bronchioloalveolar carcinoma. At lower magnification, α-smooth muscle actin-positive cells could be seen in the area of bronchioloalveolar carcinoma, but rarely seen in the adjacent normal lung (a). Subepithelial myofibroblasts positive for α-smooth muscle actin abruptly appear at the interface between normal lung and bronchioloalveolar carcinoma. α-smooth muscle actin staining in normal alveolar septa represents vascular pericytes (b). In pure bronchioloalveolar carcinoma, a thin layer of slender subepithelial myofibroblasts was observed in the alveolar septa (c). At higher magnification, the cells were located immediately beneath the cancer cells (d).