MUC5AC and neoplasm: The histologic peritoneal regression grading score (PRGS) [18] demonstrated no patients with grade 4 or no response (no regression and tumor cells visible at lowest magnification), 5 patients with grade 3 or minor response (tumor cells predominant over fibrosis), 2 patients with grade 2 or major response (regressive changes such as necrosis, fibrosis, or acellular mucin predominant over tumor cells), and 2 patients with grade 1 or complete response (no tumor cells, only abundant fibrosis, acellular mucin, or necrosis).