Congruously, another study also discovered FAP expression on M2 macrophages in a transplanted model of pancreatic ductal adenocarcinoma, promoting tumoral immune suppression [17]; thus, it is inferred that collagen I helps maintain the M2 phenotype of macrophage infiltration in the tumor microenvironment with high expression of FAP, and the M2 phenotype is the anti-inflammatory phenotype of macrophages that suppresses immunity and enhances tumor proliferation [34]. Here, FAP is linked to pancreatic ductal adenocarcinoma.