UNLABELLED: The integrin alpha(v)beta(3) is a key player in angiogenesis and metastasis. Our aim was to study the uptake patterns of the alpha(v)beta(3)-selective PET tracer (18)F-galacto-RGD in invasive ductal breast cancer. METHODS: Sixteen patients with primary (n = 12) or metastasized breast cancer (n = 4) were examined with (18)F-galacto-RGD PET. Standardized uptake values (SUVs) were derived by region-of-interest analysis, and immunohistochemistry of alpha(v)beta(3) expression was performed (n = 5). RESULTS: (18)F-Galacto-RGD PET identified all invasive carcinomas, with SUVs from 1.4 to 8.7 (mean +/- SD, 3.6 +/- 1.8; tumor-to-blood and tumor-to-muscle ratios, 2.7 +/- 1.6 and 6.2 +/- 2.2, respectively). Lymph-node metastases were detected in 3 of 8 patients (mean SUV, 3.3 +/- 0.8). SUVs in distant metastases were heterogeneous (2.9 +/- 1.4). Immunohistochemistry confirmed alpha(v)beta(3) expression predominantly on microvessels (5/5) and, to a lesser extent, on tumor cells (3/5). CONCLUSION: Our results suggest generally elevated and highly variable alpha(v)beta(3) expression in human breast cancer lesions. Consequently, further imaging studies with (18)F-galacto-RGD PET in breast cancer patients for assessment of angiogenesis or planning of alpha(v)beta(3)-targeted therapies are promising.