Intraductal Oncocytic Papillary Neoplasms: Clinical-Pathologic Characterization of 24 Cases, With An Emphasis on Associated Invasive Carcinomas

Abstract

Background: Intraductal oncocytic papillary neoplasm (IOPN) of the pancreas is a rare tumor. Recent molecular data indicate that it is distinct from other intraductal neoplasms; however, its clinicopathologic characteristics, especially the frequency/significance of an invasive carcinoma component, and biologic behavior remain to be fully defined.

Design: Clinicopathologic characteristics and survival of 24 IOPNs were analyzed. By definition, all tumors exhibited intraductal growth and oncocytic morphology.

Results: The female:male ratio was 1.7, and mean age was 59. In 44% of the patients, the IOPN was discovered incidentally; however, the working diagnosis was "ductal adenocarcinoma" in 42%. Fourteen IOPNs occurred in the head of the pancreas. The median tumor size was 4.5 cm. The tumors often grew along adjacent benign ducts, mimicking invasion, but only 29% exhibited unequivocal invasive carcinoma, mostly in the form of microscopic foci (pT1a=4, pT1b=1, pT2=2), and only 6% had lymph node metastasis. Invasive carcinoma was predominantly composed of small tubular units lined by oncocytic cells, or individual oncocytic cells infiltrating the periductal stroma. Follow-up information was available for 18 patients (median=6.8 y). No patients died from the disease, and the overall 10-year survival was 94%. Patients with invasive carcinoma trended toward a lower 5-year recurrence-free survival than those with noninvasive IOPNs (66% vs. 93%, P=0.066), but overall survival was not impacted by the presence of invasion (P=0.38).

Conclusions: IOPN is a distinct tumor type in the pancreas. Despite its morphologic complexity and often extensive pagetoid spread to adjacent ducts, conventional invasive carcinoma is seen in only 29% and usually as microscopic foci. Thus, it is not surprising that IOPN exhibits indolent behavior even when invasion is present.

Figure 1.

Macroscopic picture of IOPN with cyst lined by papillary excrescences.

Figure 2.

On microscopy, the lesion exhibits papillary architecture (A) with distinct oncocytic cytology and intracytoplasmic lumens (B).

Figure 3.

IOPNs can invade as small infiltrative tubules of oncocytic cells (A), as mucinous tumors with free-floating oncocytic cells (B), or as large pushing nodules (C).

Figure 4.

IOPNs may exhibit pseudo-invasive patterns including growing along adjacent benign ducts (arrow head) (A), or myxoid stroma changes that simulate desmoplasia (B). If present, abrupt transition (star) from a morphologically normal epithelium to oncocytic epithelium within the same duct is helpful in recognizing pseudoinvasion (C). Tangential sectioning also mimics invasion by creating a complex appearance (D).