Invasive low-grade papillary urothelial carcinoma: an immunohistochemical study of 26 cases

Invasive low-grade papillary urothelial carcinoma (LGPUC) is rare. We studied the immunohistochemical (IHC) expressions of CK20, p53, E-cadherin, phosphatase and tension homolog (PTEN), and Ki-67 in both noninvasive and invasive components in 26 cases. In the noninvasive component of LGPUC, 81% showed CK20 expression, and 50% showed p53 labeling. There was a wide range of Ki-67 labeling from less than 5% to 70%. All cases had intact PTEN except 1 that showed focal clonal PTEN loss in both noninvasive and subjacent invasive components. All cases had preserved strong and diffuse E-cadherin expression in both noninvasive and invasive components. There was no significant change between the noninvasive and invasive components in the IHC labeling of these markers, although 7 (33%) of 21 cases showed decreased CK20 expression to a certain extent in the invasive component. Only 2 cases showed significant increase of p53 expression in the invasive component compared with the noninvasive component. Two cases showed increase of Ki-67 labeling from less than 5% in the noninvasive to 20% and 40%, respectively, in the invasive component. High Ki-67 labeling was present in a significant portion of invasive LGPUC cases in both noninvasive and invasive components, much higher than in previous studies of noninvasive LGPUC. Whether higher Ki-67 in these cases is associated with more aggressive disease warrants further study. In general, it is not very helpful to use immunostains in diagnosis and predicting prognosis. This is the largest series to study the IHC characteristics of this entity.