A comparative study of histopathology, hormone receptors, peanut lectin binding, Ki-67 immunostaining, and nucleolar organizer region-associated proteins in human breast cancer. The current study was performed on 71 cases of human female breast cancer and compares the results of five morphologic methods developed for the detection of estrogen receptors (ER), progesterone receptors (PgR), lectin Peanut agglutinin (PNA) binding sites, monoclonal antibody Ki-67 immunoreactivity, and the mean number of argyrophilic nucleolar organizer regions (Ag-NOR). All the parameters were evaluated on serial cryostat sections representative of a closely related, if not identical, neoplastic population. A significant positive correlation was found between the occurrence of estrogen, progesterone, and peanut receptors and between Ki-67 immunoreactivity, mean number of NOR, and mitotic index. Furthermore, ER, PgR, and PNA receptors showed a significant, inverse correlation with Ki-67 immunoreactivity, mitotic index, and mean number of Ag-NOR. These results provide further data that support the hypothesis that (1) progesterone and PNA receptors are estrogen-induced and indicate a metabolic response of the target cells to functioning estrogen receptors; (2) the mean number of NOR reflects the cell kinetics of the tumor; and (3) metabolic differentiation of neoplastic cells is inversely correlated to the proliferation index. 