Figure 1.

TNBC xenograft tumor is associated with severe hypoxia. Oxygen concentration (pO₂) was measured by in vivo EPR oximetry in triple-negative breast cancer (TNBC) xenograft tumors, developed in mice using MDA-MB-231 cells. (A) Representative tracings of tumor pO₂ values in mice breathing room air and 100% oxygen. In both cases, the mice were kept in room air for about 20 min, the breathing gas was switched to 100% oxygen at the time point indicated by the up-arrow and returned to room-air breathing 20 min later (indicated by down-arrow). In one case (red tracing), the tumor pO₂ increased from about ~2 mmHg to ~8 mmHg at the end of 20 min of 100% oxygen administration, while in the other case (black tracing) the tumor oxygen was at ~4 mmHg and was non-responsive to hyperoxygen breathing. (B) Tumor pO₂ values (Mean ± SEM, N = 4) measured over growth period. (C) Tumor volume (Mean ± SEM, N = 27) measured over growth period. (D) Relationship between tumor pO₂ (Mean ± SEM of measurement) and volume for individual tumors. There is no correlation between tumor pO₂ and volume (r = 0.269).