SPARC and neoplasm: To determine whether the matrix detected by PAS staining included collagen, tumor sections were subjected to immunohistochemical analysis using an antibody that detects only human procollagen I. Both the control and the SPARC-expressing tumors expressed procollagen I. However, the SPARC-expressing tumors were more intensely stained, suggesting greater levels of procollagen I synthesis (Fig. 1b).