Direct oxygen partial pressure (pO₂) readings in breast cancers, in fibrocystic disease, and in the normal breast have been obtained using a novel technique which allows for the systematic evaluation of the oxygenation status as a function of pathological staging and histological grading. Measurements were performed in awake pre- and postmenopausal patients with well-defined arterial blood gas status.

The measuring procedure encompasses a computerized electrode movement in the tissue which avoids significant compression artifacts and allows routine measurement in human tumors before, during, and after treatment. Using this reliable technique, pO₂ measurements in the normal breast and in fibrocystic disease resulted in oxygenation patterns which were characteristic for normal, adequately supplied tissues. The median pO₂ values were 65 and 67 mm Hg, respectively, with no pO₂ readings below 12.5 mm Hg in the normal breast, and ≤5 mm Hg in fibrocystic disease, respectively. In contrast, in breast cancers the median pO₂ value was 30 mm Hg (pooled data for pathological stages T₁-T₄). To date, 6 of 15 breast cancers exhibited pO₂ values between zero and 2.5 mm Hg, i.e., tissue areas with less than half-maximum radiosensitivity. The oxygenation pattern in breast cancers and the occurrence of hypoxia and/or anoxia did not correlate with either the pathological stages and histological grades or with a series of clinically relevant parameters. No significant differences were found between pre- and postmenopausal tumors and between lobular and ductal carcinomas. Tumor-to-tumor variability in the oxygenation pattern was more pronounced than intratumor heterogeneity. pO₂ variations within a tumor cannot be predicted, e.g., as a function of the measuring site (tumor center versus periphery).