Infiltrating components of IDC of the pancreas show duct-like structures combined with tubular neoplastic glands [4]. Therefore, in well-differentiated IDC, distinguishing between the intraductal component and the space circumscribed by the infiltrating component can be extremely difficult [2]. The incidence of intraductal components of IDC has been reported to be 59% by other authors [3, 4, 6-9, 13]. We showed that 69% of IDC cases were accompanied by intraductal components with the following methods [14]. It is known that pancreatic ductal systems contain elastic fibers in the wall, and that ductal mural elastic fibers are preserved even in some pathological states [14-17] (fig. 1). Intraductal components of IDC can be clearly identified by visualizing mural elastic fibers and emphasizing the contour of ductal systems on elastica van Gieson (EVG)-stained sections (fig. 2). Ducts showing infiltrating components should be carefully excluded (fig. 3). Only ducts which are not continuous with infiltrating components of IDC and whose wall structures are completely preserved are selected. Carcinoma foci in these ducts are defined as intraductal components of IDC. The intraductal component of IDC is distinguished from

Fig. 1. Low power field of IDC (EVG). Note the well-preserved ductal mural elastic fibers.
Fig. 2. The elastic fiber contour of the ductal system (a HE, b EVG). Intraductal components rimmed with ductal mural elastic fibers and infiltrating components without ductal mural elastic fibers.
Fig. 3. Intraductal invasion (a HE, b EVG). The ductal mural elastic fibers are destroyed locally by infiltration of IDC.

atypical hyperplasia by the application of generally accepted published criteria [1, 2, 4, 12]. Duct-like structures that are not rimmed with elastic fibers imply infiltrating components of IDC.

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