Paraffin-embedded primary tumor specimens from 48 patients with breast cancer were examined for DNA ploidy, S-phase fraction (SPF), and concanavalin A (Con A) reactivity. The results were correlated with clinicopathological prognostic factors, including patients' age and menopausal status, stage of disease, nuclear grade, and size of the primary tumor. There were no associations among ploidy, SPF, Con A reactivity, and menopausal status, stage of disease, or size of the primary tumor. However, among patients who were 50 years or older, 81% had diploid tumors and 73% had good reactivity (3 + or better staining score) with Con A. In contrast, among patients who were younger than 50 years, 45% had diploid tumors (P < 0.05) and 21% had good Con A reactivity (P < 0.05). Seven of 19 (37%) poorly differentiated tumors and 7 of 9 (78%) moderately differentiated tumors had good reactivity with Con A (P < 0.05). Reactivity of tumor cells with Con A in primary breast cancer tissues deserves further evaluation as a potential biomarker of prognosis. (C) 1994 Wiley-Liss, Inc.