The present study was designed to analyze the expression of lectin-binding sites for peanut agglutinin (PNA) in paraffin sections of primary invasive ductal carcinoma not otherwise specified and to consider PNA lectin histochemistry as a further aid in the prognostic evaluation of breast cancer. The expression of lectin-binding sites was studied using the avidin-biotin complex/ immunoperoxidase technique, and analyzed in relation to the different clinical, pathological, and biological parameters of the primary disease, i.e. the presence or absence of nodal metastases, pre- or post-menopausal age, size of the tumor, mitotic activity index, morphometric prognostic index, DNA content, S-phase fraction, and steroid receptor status. The results show significant differences in PNA binding patterns among malignant epithelial breast cells. There was no expression of PNA-binding sites in 14 out of 157 tumors, while 64 showed mostly apical (membrane) staining and 124 non-apical (membrane and/or cytoplasmic) staining. Apical staining was mostly observed in patients without lymph node metastasis, with positive steroid receptor status, and those who were postmenopausal diagnosis; non-apical staining was mostly observed in lymph-node-positive premenopausal patients negative for steroid receptors and with aneuploid tumor cells. Our results indicate that, in malignant breast cells, there is an alteration of cell-surface glycoconjugates, shown by heterogeneity within a histopathologically defined group, which is related to different properties of tumor cells. The apical PNA binding pattern indicates a better differentiation of tumor cells while non-apical PNA binding suggests a higher metastatic potential. Specific PNA lectin binding patterns should be considered as a further reliable prognostic factor in breast cancer.