The matrix metalloproteinase-9 showed very strong correlation with CK19 mRNA in breast carcinoma of no special type metastases, and therefore immunohistochemical expression of this marker in SLNs should be considered as a useful method whenever the OSNA analysis for some reason is not physically available or it is not recommended for patients previously subjected to breast surgery. The gene discussed is MMP9; the disease is breast carcinoma.