To investigate the contribution of various tumor components to tumor [3H]FDG uptake, the size of proliferative cell and macrophage populations and the extent of necrosis, inflammatory infiltration and granulation tissue formation were evaluated in syngeneic rat mammary cancers (RMC) grown in immunocompetent rats, an animal tumor model that closely mimics human breast carcinoma.
Methods: Tissue components of breast cancers grown in female Lewis rats (n = 6) were identified histologically and immunohistochemically. Tracer uptake was studied by quantitative autoradiography 2 hr after an intravenous injection of 100 muCi [3H]FDG. RESULTS;: RMC tumors were glandular, with small foci of necrosis and were surrounded by a thin layer of granulation tissue. Tumors retained approximately 4% of the injected FDG dose (1.9 +/- 0.27 muCi/g). Macrophages numbered 0.5% of total cancer cells (1.2 +/- 1.0 of 246 +/- 77) and 18.0% +/- 3.9% of the nuclei of cancer cells were proliferating cell nuclear antigen (PCNA) positive (52 +/- 27 of 293 +/- 55). FDG uptake (in apparent disintegrations per minute per microgram of protein) in the cancer cell was 47.3 +/- 5.6, with the highest uptake in foci of high tumor cell density (82.1 +/- 6.3). Lower levels of FDG uptake were found in necrotic areas (19.8 +/- 22.9), granulation tissue (26.9 +/- 9.2) and areas of inflammatory infiltration (20.5 +/- 15.5).
Conclusion: These data suggest that FDG-PET imaging of untreated breast cancer mainly reflects tracer uptake in cancer cells.