NOS2 and colon carcinoma: Further analysis of the primary human colon carcinoma tissues revealed three types of iNOS expression patterns: 1) only tumor cells are iNOS-positive and no adjacent immune cells contain iNOS (Fig. 2a); 2) tumor cells exhibit undetectable iNOS, but adjacent immune cells express iNOS (Fig. 2b); and 3) both tumor cells and adjacent immune cells have detectable iNOS protein (Fig. 2c).