BACKGROUND AND OBJECTIVES: Axillary lymph node status is the most important prognostic factor in patients with operable breast cancer. Recent studies have demonstrated the possibility of identifying the sentinel lymph node (sN) as a reliable predictor of axillary lymph node status in both cutaneous melanoma and breast cancer. Sentinel lymph node identification proved feasible by either peritumoral dye injection (Patent Blue-V) or radiodetection, with identification rates of 65-97% and 92-98%, respectively. However, some important issues need further definition, namely (a) optimization of the technique for intraoperative detection of the sN, (b) predictive value of the sN with regard to axillary lymph node status, and (c) reliability of intraoperative histology of the sN. We reviewed our experience in sN detection in patients with stage I-II breast cancer to assess the feasibility and accuracy of lymphatic mapping, by vital blue dye or radioguided surgery, and sN histology as a predictor of axillary lymph node status. METHODS: Two groups of patients (55 and 48) were recruited between May 1996 and May 1997 and between October 1997 and February 1998; the patients of the first series underwent vital blue dye lymphatic mapping only, whereas those of the second series had a combined approach with both vital blue dye mapping and radioguided detection of the sN. RESULTS: In the first set of patients, the sN was identified in 36/55 patients (65.4%); sN histology predicted axillary lymph node status with a 77% sensitivity (10/13), a 100% specificity (23/23), an 88.5% negative predictive value (23/26), and an overall 91.5% accuracy (33/36). The sN was the quasi-elective site of lymph node metastases because in clinically N0 patients nodal involvement was 20-fold more likely at histology in sN than in non-sN (30% and 1.5%, respectively). In the second set of patients, 49 lymphadenectomies were performed because 1 patient had bilateral breast cancer; the sN was identified in 45/49 lymphadenectomies (92%). The sN was intraoperatively negative at frozen-section examination in 33 cases, and final histology confirmed the absence of metastases in 31/33 cases (94%), whereas in 2 cases (6%) micrometastases only were detected. Final histology of the sN predicted axillary lymph node status with an 87.5% sensitivity (14/16), a 100% specificity (29/29), a 93.5% negative predictive value (29/31), and an overall 95.5% accuracy (43/45). CONCLUSIONS: Sentinel lymphadenectomy can be better accomplished when both mapping techniques (vital blue dye and radioguided surgery) are used. In this group of patients, agreement of intraoperative histology of the sN with the final diagnosis was 94%, and sN histology accurately predicted axillary lymph node status in 43/45 lymphadenectomy specimens (95.5%) in which an sN was identified.