IPNB have been proposed as a precursor lesion of cholangiocarcinoma (CCA), and about a half of IPNB at the time of surgical resection are associated with an invasive carcinoma [1], [2], [3], [4]. While there are many studies on the clinicopathological and molecular features of IPNB and their prototypic features are already established [5], [6], [7], [8], [9], [10], [11], [12], [13], the pathologic features of invasive carcinoma associated with IPNB remain to be clarified. In addition, a diagnosis of IPNB in the cases with considerable invasion is still controversial [6], [7], [14], [15], [16], [17].

Herein, we tried to clarify the patterns of invasive carcinomas associated with IPNB by using a total of 82 cases of IPNB, and then to correlate these invasive patterns with their post-operative overall survival (OS), referring to the T-category of TNM classification [18].