Papillary intralymphatic angioendothelioma (PILA): a report of twelve cases of a distinctive vascular tumor with phenotypic features of lymphatic vessels.

Six childhood vascular tumors were designated as "malignant endovascular papillary angioendothelioma" by Dabska in 1969. Since then, a few reports of similar cases were published, often called "Dabska tumors." Twelve similar cases were identified in review of vascular tumors from the authors' institutions. There were five men and seven women, including seven adults. Patient ages ranged from 8 to 59 years (mean, 30 years). The tumors occurred in the dermis or subcutis of the buttocks or thigh (n = 6), thumb or hand (n = 3), abdomen (n = 2), and heel (n = 1). The tumor sizes ranged from 1 to more than 40 cm (mean, 7.0 cm). The unifying feature of all cases was distinctive intravascular growth of well-differentiated endothelial cells presenting as a matchstick columnar configuration, sometimes with a large production of matrix that was positive for collagen type IV. In half the cases, these intravascular proliferations had an associated actin-positive pericytic proliferation. There was minimal cytologic atypia and rare to absent mitotic activity. Two cases had an adjacent lymphangioma, and two additional cases had clusters of lymphatic vessels adjacent to the tumor. All but two of the cases showed varying degrees of stromal or intraluminal lymphocytes. Occasional epithelioid endothelial cells were seen, but no cases had features typical of epithelioid, spindle cell, or retiform hemangioendothelioma. Tumor cells were positive for vimentin, von Willebrand factor, CD31, and focally for CD34 and were negative for keratins, epithelial membrane antigen, S-100 protein, and desmin. Vascular endothelial cell growth factor receptor type 3, a recently introduced marker for lymphatic endothelia, was positive in all eight cases that were studied, supporting a lymphatic phenotype. Follow-up in 8 of the 12 cases showed no evidence of recurrences, metastases, or residual disease during follow-ups ranging from 1 to 17 years (mean, 9 years). Based on the proliferative borderline features and the lymphatic phenotype, we propose to designate these tumors as papillary intralymphatic angioendothelioma. Additional cases with extensive follow-up should be studied to rule out variants with malignant potential.