Novel Morphologic and p16 and p53 Immunohistochemical Features of Papillary Intralymphatic Angioendothelioma (PILA) of Dabska: A Case Report and Literature Review

Summary: Papillary intralymphatic angioendothelioma (PILA) of Dabska is a very rare vascular tumor of low malignant potential, with less than 50 cases reported in the literature. Despite decades of research interest, little is known about its pathogenesis. Herein we report a man in his 20s with a 1 cm vascular lesion on the left buttock. Excision specimen showed a dermal vascular neoplasm with 2 components: Centrally, there were large intraluminal papillary projections with hobnail morphology and hyalinizing stroma; Peripherally, there were small vasoformative cell groups. The tumor cells in both components were positive for CD31 and podoplanin, consistent with PILA, while negative for synaptophysin. Interestingly, p16 showed variable but stronger staining of the small vasoformative cell groups compared to the central papillae, with cytoplasmic staining showing central lumens. p53 were of similar findings. In contrast, neither p16 nor p53 was positive in the background vessels. Based on these findings, it is plausible that PILA advances peripherally as small vasoformative groups with high p16 and p53 expression reactive to oncogenic driving forces, leaving more mature papillary structures centrally. Our findings expand the literature with novel morphologic and immunohistochemical findings and provide novel insights into the pathogenesis of PILA.