Immunodetection of the metastasis-associated laminin receptor in human breast cancer cells obtained by fine-needle aspiration biopsy. Fine-needle aspiration biopsy of the breast is a very useful technique for the evaluation of a suspect lesion before surgical removal. Increased expression of the 67-kd laminin receptor has been associated with the metastatic phenotype of cancer cells, particularly in colon and breast cancers. In this study, the expression of laminin receptor was evaluated using the immunoperoxidase technique in 81 breast aspirates (26 benign and 55 neoplastic lesions). Cells obtained from benign samples exhibited a low level of laminin receptor antigen detected by affinity-purified antibody raised against a cDNA-derived laminin receptor peptide. In contrast, 71% of smears obtained from malignant breast lesions contained cells that were strongly stained by the antibody. Heterogeneous expression of the laminin receptor was noted in both breast aspirates and fixed tissue specimens. These data suggest that the immunodetection of laminin receptor in cells obtained by fine-needle aspiration of breast lesions could be a valuable adjunct in the prognostic evaluation of breast lesions. 