PECAM1 and retroperitoneal sarcoma: Slices from eight retroperitoneal sarcomas prepared immediately after surgery (well differentiated liposarcoma, n = 4; undifferentiated sarcoma, n = 2; and leiomyosarcoma, n = 2) were treated with or without TNF-α for 90 min, washed and then maintained in fresh medium without TNF-α for 72 h before TUNEL assay and subsequent labelling with anti-CD31 antibody and TO-PRO3.