We aimed at developing a more detailed understanding of cyclin D1 in early stage human breast cancer and defining the biologic profiles with different prognostic value correlating cyclin D1 gene amplification and chromosome 11 aneusomy with bio-pathologic variables of known clinical importance. Cyclin D1 gene amplification and chromosome 11 aneusomy were investigated using fluorescence in situ hybridization whereas cyclin D1, PgR, HER-2, Bcl2, p53, and Ki-67 expressions were analyzed by immunohistochemistry in 121 stage I or II breast cancer patients uniformly treated with cyclophosphamide/metotrexate/5-fluorouracil-based chemotherapy. Cyclin D1 was amplified in 6.6% and overexpressed in 32.2% of cases. Amplification was not associated with any selected bio-pathologic variables, whereas the chromosome 11 aneusomy level significantly increased in tumors with higher histologic grade (P 30%, ratio (cyclin D1 gene/CEP11) > 2, was associated with tumor relapse defining the most unfavorable biologic profile. Kaplan-Meier's method showed significantly shorter disease-free survival in patients with at least 3 variables positive out of the 6 detected by multiple correspondence analysis. In multivariate analysis, the identified biologic profile emerged as the only significant prognostic indicator. Our findings are of particular clinical interest for early stage breast cancer patients, because the assessment of biologic factors predictive of tumor aggressiveness may influence postoperative therapeutic strategies.