accumulatedmore in cancer cells and less in infiltratingfibroblastsand macrophages in alltumor models.Irradiationsignificantlydecreased @mTc-MlBl uptake, but a rapid increasewas noted at recurrenceon day 7. Changes in FDG uptake were not significant at recurrence. Microvesseldensity in tumor tissue correlated significantlywith

@“Tc-MIBI uptake in breast cancer in 1992 (2), there has been continued interest in the evaluation of breast cancer using this radiopharmaceutical agent. Various groups have reported the clinical usefulness of @Tc-MIBIscintimam mography. In particular, @†̃Tc-MIBI scintimammography hasbeen usedto detect tumors in patients with densebreasts, to evaluate chemotherapeutic response, and to predict multi drug resistance (3—6). Cellular accumulation of @Tc-MIBI has been shown to correlate with the level of P-glycoprotein expression. P-glycoprotein, a product of the mdr gene, is well known to actively expel @Tc-MIBIfrom tumor cells through an efflux pump using adenosine triphosphate (5,7— 9). However, only a few studies have evaluated the accumu lation and distribution of@Tc-MIBI within tumors negative for P-glycoprotein. Angiogenesis is an important process in the proliferation and metastasis ofbreast carcinoma (10—13),and immunohis tochemically determined microvessel density has been used asa prognosticindicatorof breastcancer(11—13). However, to our knowledge, the correlation between angiogenesis and the magnitude of tumor @Tc-MIBIuptake has not been evaluated. Our aim was to evaluate intratumoral accumulation and distribution of @°@Tc-MIBI and to compare it with either 2-deoxy-D-[1-@C]-glucose (@C-DG) or FDG using 3 animal models of breast cancer. We also investigated the effects of irradiation on @†̃@Tc-MIBI uptake and evaluated the correla tion between microvessel density and @Tc-MIBIuptake.