The nucleus (N) of the neoplastic Type II pneumocyte contains central and peripheral clumps of heterochromatin. Vacuoles and clefts in the cytoplasm of the neoplastic Type II pneumocyte are interpreted as an artifact of fixation. An external lamina separates these cells from mesenchymal cells (arrowheads), blood vessels and collagen in the tumor septa. The mesenchymal cells contain prominent rough endoplasmic reticulum and focal pools of glycogen (G).