Distribution and clinical significance of tumour-associated macrophages in pancreatic ductal adenocarcinoma: a retrospective analysis in China

Background We aimed to characterize the localization and prognostic significance of tumour-associated macrophages (TAMS) in pancreatic ductal adenocarcinoma (PDAC). Methods Tumour specimens from 70 patients with PDAC and inflammatory specimens from 13 patients with chronic pancreatitis were collected and analyzed for TAM and M2 macrophage counts by immunohistochemistry. Correlations between TAM distributions and clinicopathologic features were determined. Results Immunohistochemical analysis showed that TAM and M2 macrophage counts were higher in tissues from PDAC than from chronic pancreatitis. The TAMS and M2 macrophages both infiltrated more into peritumour. Both macrophage types were positively associated with lymph node metastasis (p = 0.041 for TAMS in peritumour, p = 0.013 for M2 macrophages in introtumour, p = 0.006 for M2 macrophage in peritumour). In addition, abdominal pain was significantly more frequent in PDAC patients with a greater TAMS count. The survival rate was much lower in patients having high infiltration by M2 macrophages than in those having low infiltration. Conclusions The TAM count might be associated with neural invasion in PDAC, and M2 macrophages might play an important role in lymph node metastasis. Higher counts of either macrophage type were associated with increased risk of lymph node metastasis, and the M2 macrophage count could potentially be a marker for evaluating prognosis.