The success of current hormonal therapies used in breast cancer patients often depends on estrogen receptor (ER) status. The simultaneous pathological assessment of primary breast tumors (PTs) and metastases to regional lymph nodes (MRLNs) could improve the effectiveness of this treatment, but is rarely performed. Consequently, we studied by immunohistochemistry the expression of ERalpha (ERalpha), ERbeta (ERbeta), and the proliferation marker (Ki-67) in PTs and matching MRLNs. The expression of each ERalpha, ERbeta, and Ki-67 positively correlated between PTs and MRLNs (r=0.751, p<0.0001; r=0.391, p<0.03; and r=0.707, p<0.0001, respectively). A negative correlation between the expression of ERalpha and Ki-67 was found in PTs (r=-0.678, p<0.001) and MRLNs (r=-0.501, p<0.005). A negative correlation between ERalpha and Ki-67 was also observed in PTs vs. MRLNs (r=-0.619, p<0.0001). Moreover, the expression of ERalpha and Ki-67 was not associated with nodal status, contrary to ERbeta expression, which correlated with negative axillary node status. The results indicated that the associations among ERalpha, ERbeta, and Ki-67 are maintained in PTs and MRLNs. Thus, simultaneous assessment of selected markers in PT and MRLN might help in understanding the mechanisms of breast cancer progression as well as result in the development of new principles for diagnosis and individual therapy planning of estrogen dependent cancer.