The early state of invasive pancreatic ductal adenocarcinomas: characteristics of the low papillary type and flat type intraductal carcinoma.

OBJECTIVE

To analyze the early state and the mode of advancement of IPDACs.

METHODS

Eighty-two cases of IPDAC were resected, and the noninvasive cancer parts were identified pathohistologically. According to the pancreatic intraepithelial neoplasia (PanIN) classification, noninvasive cancer parts were equivalent to PanIN-3; the noninvasive cancer parts in the invasive area and noninvasive intraductal spread (NIIDS) area were histologically examined. Noninvasive intraductal spread means a diffuse PanIN-3 change that extended continuously outward from the invasive area. In cases with NIIDS, the length of NIIDS was measured.

RESULTS

Histologically, the noninvasive cancer parts were categorized into 3 types: flat (F), low papillary (LP), and mixed (flat and low papillary [FLP]) types; each type comprised 18.3%, 34.1%, and 47.6%, respectively. Cases with NIIDS of 2 mm or more were found in 56.1% of all the patients, and the F, FLP, and LP types comprised 13.3%, 59.0%, and 75.0%, respectively. The maximal NIIDS lengths were 10, 40, and 80 mm with averages of 1.5, 5.7, and 12.5 mm in the F, FLP, and LP types, respectively. The cases with the LP component revealed positive NIIDS and longer NIIDS lengths more frequently than those without the component (F type) (P < 0.001). The survival rates of the F, FLP, and LP types showed no statistical difference. The prognosis was better in cases of less advanced stages.

CONCLUSIONS

The noninvasive cancer parts (PanIN-3 lesions) of IPDACs were divided into 3 types: F, LP, and mixed types; the LP type had a greater tendency than the F type to spread intraductally. The LP type seemed to change to invasive cancer after or while spreading intraductally to some extent, whereas the F type seemed to invade with little intraductal spread.