Primary chemotherapy represents an ideal model to evaluate the relationships between treatments and the prognostic and predictive parameters provided by the new technologies. First- and second-generation trials have shown that primary chemotherapy significantly improves the rate of breast conservation without increasing the risk of ipsilateral recurrence and while assuring survival rates comparable with those achieved with postoperative chemotherapy. Moreover, patients who exhibited a pathologic complete response (pCR) showed better progression-free survival and overall survival. The third-generation trials were aimed at improving the percentage of pCR, identifying and validating gene and protein biomarkers of chemotherapy sensitivity, and better defining the individual risk of relapse. Several parameters, such as index of proliferation and apoptosis, expression of proteins (eg, p53 and Bcl-2), and hormone receptor and epidermal growth factor family receptors, have been related to response to primary chemotherapy. Negative hormone receptors and greater proliferative activity seem to be the only parameters more consistently associated with greater chemotherapy sensitivity. However, the strength of this association is not sufficient to differentiate patients at different degrees of risk and does not allow for an individualized therapeutic choice. Newer technologies offer the possibility of evaluating thousands of genes and identifying clusters of gene expression associated with significantly different risks of relapse and patterns of sensitivity/resistance to specific drugs. The primary chemotherapy model is the ideal clinical setting in which to validate the relationship between tumor molecular profiling and treatment outcomes and to design tailored therapies based on observed effects on individual tumors.