Phosphomannose Isomerase High Expression Associated with Better Prognosis in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death in the United States. The need for increased patient survival has not been met for PDAC. The addition of mannose to conventional chemotherapy leads to accumulation of mannose metabolite in cancer cells and increases subsequent cell death. This susceptibility to mannose depends on the levels of phosphomannose isomerase (PMI). The cancer cells with lower levels of PMI are more sensitive to mannose than cells with higher levels. In this study, we investigated the association of PMI expression with clinical and pathological features of PDAC cases.

PMI antibody immunohistochemistry (AbCam) was performed on tissue microarrays from 235 PDAC by a standard protocol on Ventana automated immunostainer. The PMI intensity was graded (0-3) and the proportion of positivity was scored. Correlation of PMI expression with staging and survival was analyzed.

Of the 235 cases, 51.5% (n=121) cases demonstrated grade 2 intensity with 90.1% of these (n=109) showing positivity in ≥70% of tumor cells. Ninety-eight (41.7%) cases exhibited grade 3 intensity with 94.9% (n=93) of these cases showing ≥70% reactivity. Sixteen cases (6.8%) were nonreactive (intensity grade 0-1). Intensity of PMI expression was associated with significantly better prognosis as assessed by median survival in months (M): grade 0-1 intensity group: 11.2 M; grade 2 intensity group: 25.2 M; and grade 3 intensity group: 33.2 M (p=0.03). A minority (6.8%) of PDACs show non-high PMI expression with poorer prognosis.

Mannose may be a particularly useful adjunct with chemotherapy to treat this aggressive subgroup. PMI expression is also a potential biomarker to predict the prognosis of PDAC.