Recent evidence attributed important influence of chemokines and their receptors on motility, homing, and proliferation of cancer cells at specific metastatic sites. Here we report that the CXCL12 (SDF-1alpha) chemokine receptor CXCR4 is expressed in human ductal carcinoma in situ (DCIS) as well as in atypical ductal hyperplasia. CXCR4 was expressed in pure DCIS and DCIS with concurrent invasive disease. In 66% of the samples, atypical ductal hyperplasia was present, and > 92% exhibited positive CXCR4-staining. Expression of CXCR4 at this very early step of tumor development indicates a role of this receptor in providing a selective advantage to such cells on their way to metastasizing carcinomas. These results strengthen the ideas to target chemokine networks involved in tumor progression and metastatis as a therapeutic approach in malignant disease or as a chemoprevention strategy, blocking the transition from premalignancy to malignancy.