The concentration of bleomycin labeled with Co‐57 in primary and metastatic tumors

The concentration over time of bleomycin labeled with Co‐57 was measured in 39 primary and metastatic tumor sites in 16 patients using a newly developed and validated single photon emission computed tomography (SPECT) method. There were nine primary tumors, 15 metastatic tumors, and five multifocal lymphomas. Co‐bleomycin concentrations also were measured in primary and metastatic B‐16 melanoma tumors in mice. In humans, metastases to lymph nodes (1.58 ± 0.51 %ID/ml × minutes) showed significantly higher (P < 0.01) tumor cumulative concentrations of Co‐bleomycin than metastases to liver, bone, lung, and brain (0.76 ± 0.20 %ID/ml × minutes). The cumulative concentrations of Co‐bleomycin in human lymphomas (1.1 ± 0.25 %ID/ml × minutes) also were significantly higher (P < 0.01) than the concentrations in human metastases other than lymph nodes. The cumulative concentration in cerebral metastases (0.65 ± 0.18 %ID/ml × minutes) was significantly lower (P < 0.05) than in noncerebral metastases (1.22 ± 0.53 %ID/ml × minutes). Primary tumors in humans showed higher concentrations of Co‐bleomycin than metastases, except for lymph nodes. In contrast with humans, murine metastases showed higher concentrations of Co‐bleomycin (6.20 ± 2.65 %ID/g) than primary tumors (2.94 ± 0.90 %ID/g) (P < 0.001). The concentrations of Co‐bleomycin in murine tumors that were affected by bleomycin were about three orders of magnitude higher than in human tumors. The results of this in vivo study document the differences in drug delivery of Co‐57‐labeled bleomycin to human primary and metastatic tumors and show differences in drug delivery between human and murine tumors.