Eppendorf Polarographic Oxygen Data

For a subset of the tumors from client-owned dogs, tissue hypoxia levels measured with the Eppendorf polarographic oxygen technique were available from a previous trial [7] along with tumor biopsies taken at the same time point and in the same tumor region. Formalin-fixed tissue blocks were available from the latter to evaluate the immunohistochemical markers. Owner consent had been obtained for that study, which was approved by the Animal Ethics Council of the Canton of Zurich, Switzerland. Eppendorf data consisted of multiple measurements in anesthetized dogs. Tumor oxygen partial pressure measurements were performed as previously described [10, 15] with a pO2-Histograph (Helzel Medical Systems, Kaltenkirchen, Germany). The probe was calibrated before each use, and then the needle electrode was placed into the tumor tissue under ultrasound guidance (ATL 5000, Philips Medical Systems, Zurich, Switzerland). A minimum of three different electrode tracks and a minimum of 50 recorded values were acquired. The oxygenation status of each individual tumor was described using the median pO2 and the hypoxic fractions (% of pO2 values <10 mmHg, <5 mmHg and <2.5 mmHg, respectively).