Objective: One-step nucleic acid amplification (OSNA) is used in routine clinical use for sentinel lymph node biopsy (SLNB). It consists of the molecular quantitation of a tumoral marker (cytokeratin-CK 19 mRNA). Gene hypermethylation is one of the most common mechanisms of inactivation of suppressor genes. RASSF1A gene, is a region frequently hypermethylated in breast cancer. Method: 51 patients with breast cancer were included in the study, and a total of 87 lymph nodes were analysed. Results: 41 %, 33.3 % and 21.6 % of the tumours were of low, intermediate and high-grade, respectively. In 40.8 % of the cases there are not tumoral cells, in contrast to 12.2 %, 4.1 %, 14.3 %, 28.6 % that showed low number of cells/ITC (<250 copies/sample), Micro-(<5000 copies/sample) and Macro-Mtx, respectively. There is a very clear association between RASSF1A hypermethylation and the presence of tumoral cells (p= 0.004), being more frequent in Macro-mtx compared to the rest of groups (P=0.007). RASSF1A hypermethylation is also correlated to unfavorable histologic grade in the tumour (P=0.025) and lymph node involvement at the diagnosis (0.001). Conclusion: The analysis of RASSF1A hypermethylation could provide additional information to OSNA to detect tumoral cells in lymph nodes. The spare tissue material derived from OSNA could be good material to consider new molecular studies. Results: Of these, 15 patients (88,23 %) had palpable tumor at presentation, 12 (70,58 %) with palpable axillary adenopathy. In 10 cases (58,82 %) the tumor diameter was over 2 cm at the time of diagnosis. In 15 cases (88,23 %) the histological type was infiltrative ductal carcinoma, with 13 cases having high grade. Most of the tumors expressed ER and PR and were Her-2 negative (none was triple negative). However, in 11 cases (64,70 %) the ki-67 index was more than 50 %. Conclusion: Young women with breast cancer have been shown to have a poorer prognosis because of the high grade and hormonal status. Our study shows some similar aspects, but the hormonal status is totally different from the dates in the literature, revealing a possible better response to hormonal treatment and a better survival.