Measurement of tumor hypoxia in spontaneous canine sarcomas

We used positron emission tomography (PET) with [F-18]fluoromisonidazole (118 F]FMISO) to study tumor hypoxia in six dogs with spontaneous sarcomas. The tumors were regarded as hypoxic if [F-18]FMISO uptake exceeded normal tissue radioactivity by 40% (tumor/muscle ratio > 1.4) or if kinetic analysis indicated a positive [F-18]FMISO tissue influx rate (K-i>O) by a Patlak plot. Using these criteria, we found hypoxia in a fibrosarcoma grade 11, an undifferentiated sarcoma, and an ostoeosarcoma, but not in a fibrosarcoma grade I, another osteosarcoma, and a myxosarcoma. In three animals, the tumor oxygen partial pressure (pO(2)) was also measured invasively using Eppendorf needle electrodes. In these cases, the Eppendorf measurements were confirmed by the [F-18]FMISO PET results. In addition, [O-15]H2O PET was performed in four dogs in order to assess tumor perfusion. Comparisons of the [F-18]FMISO with [O-15]H2O PET images in two cases showed that tumor hypoxia occurred in the tumor center with low perfusion, whereas perfusion was heterogeneous in a nonhypoxic tumor.