The incidence and prognostic relevance of bone marrow (BM) and leukapheresis (PBPC) tumor cell contamination (TCC) in breast cancer patients is still to be circumstantiated. We developed a new comprehensive gene expression panel to study cytokeratins (CK), maspin (MAS) and mammaglobin (MAM) as possible predictors of prognosis. Forty-eight patients undergoing high dose chemotherapy (HDCT) and PBPC support were enrolled and analyzed for TCC on 116 PBPC apheresis and 96 BM obtained at basal conditions. All of the patients were evaluated by reverse transcriptase nested PCR (RT-PCR) for MAM and MAS gene expression and by immunocytochemistry (ICC) and nested RT-PCR to evaluate CK expression. PBPC and BM frequency of CK-positive (+) cells was 12-13% by ICC and 71-73% by RT-PCR respectively. Sixty-seven percent of CK ICC+ samples were MAM RT-PCR+ and 89% of them were MAS RT-PCR+. PBPC and BM frequency of MAM+ cells was 21% and 31% respectively, while for MAS+ cells it was 48% and 52% respectively by RT-PCR. After 71 mo median FU, 16 patients (33%) relapsed and 14 (88%) had BM/PBPC TCC. No marker had an impact on overall survival (OS) but MAS expression on BM and MAM expression on PBPC correlated with a statistically significant improved (p=0.05) and worsened RFS (p=0.06) respectively. These data confirm the activity of MAM as a negative prognostic factor and show for the first time that MAS could work as a tumor suppressor gene even in a clinical setting, since it protects from recurrence.