Purpose: The purpose of this study was to clarify whether the features of well-differentiated pancreatic ductal adenocarcinomas (PDACs) measuring ≤ 1 cm are the same as those of early PDACs.
Methods: Five well-differentiated PDACs measuring ≤ 1 cm were clinicopathologically compared with 19 ≥ 2 cm PDACs. Additionally, an immunohistochemical analysis for abnormalities in the expression of five molecular parameters: MUC1, p16, p53, Smad4 and sonic hedgehog, which are associated with tumor progression, was performed.
Results: The clinicopathological comparison revealed that well-differentiated PDACs measuring ≤ 1 cm were detected significantly more often without angiolymphatic invasion and with a sparse presence of cancer cells than were the ≥ 2 cm PDACs. On the other hand, in well-differentiated PDACs measuring ≤ 1 cm, the incidence of abnormal immunolabeling for MUC1, p16, p53 and sonic hedgehog was similar to that in ≥ 2 cm PDACs. However, the incidence of diffusely positive immunolabeling for MUC1 and the mean number of abnormally immunolabeled samples for the five parameters were significantly lower in well-differentiated ≤ 1 cm PDACs (20 % and 3 ± 1) than in ≥ 2 cm PDACs (90 % and 4 ± 1).
Conclusion: The current study revealed that as the tumor size increases, molecular abnormalities are accumulated, suggesting that well-differentiated PDACs measuring ≤ 1 cm are in an earlier stage of genetic progression than are ≥ 2 cm PDACs, and these lesions may exhibit early features of invasive PDACs.