Clinicopathological Analysis of Growth Patterns of Malignant Intraductal Papillary Mucinous Tumors of the Pancreas: Unusual Growth Pattern of Fistulous Extension

ABSTRACT

BACKGROUND: Usually, a malignant intraductal papillary mucinous tumor (IPMT) of the pancreas shows invasive carcinoma. Recently, IPMT with an unusual growth pattern of a fistulous extension was reported. However, little is known about malignant IPMTs with a different growth pattern of invasion and fistulous extension. METHODS: Malignant IPMTs were classified into invasive (colloid or tubular type) carcinomas and the fistulous extension type according to their growth patterns. Their clinicopathological characteristics were compared. RESULTS: Among a total of 68 cases of IPMT, there were 16 cases with malignant IPMT; eight, six and two of the colloid, tubular, and fistulous extension types, respectively. The immunohistochemical (IHC) expression of MUC1 was found in seven out of eight colloid and five out of six tubular types, but there was no IHC expression of MUC1 in the fistulous extension type. The IHC expression of MUC2 was noted in one of the eight colloid, one of the six tubular and in both cases with the fistulous extension type. There was no difference in the tumor recurrence rates bet- ween the different growth patterns. CONCLUSIONS: IPMT with the fistulous extension type has a peculiar extension pattern consisting of multiple fistulous tracts without a mass. Although most of the epithelium in the fistulous tract show moderate to severe dysplasia, only the fistulous extension should be considered to be an unusual growth pattern of malignant IPMT. The clinical significance of this unusual type of IPMT remains to be determined.