BACKGROUND The serum-soluble interleukin-2 receptor has been claimed to be a marker of host biological response in patients with solid malignancies. This study was designed to evaluate the biological significance of the preoperative serum-soluble interleukin-2 receptor concentration in patients with invasive breast cancer. METHODS Venous blood samples were collected from 66 patients with invasive breast carcinoma and the serum concentrations of soluble interleukin-2 receptor were measured with an enzyme immunoassay method. Data regarding maximum tumor diameter, age, estrogen receptor status, lymph node status, distant metastasis status, histologic grade, ploidy pattern and S-phase fraction were also collected and evaluated simultaneously with the serum concentration levels of soluble interleukin-2 receptor. Fifteen age-matched healthy subjects were used as a control group. RESULTS The mean value of serum-soluble interleukin-2 receptor in patients with invasive breast cancer was 621 +/- 145 units/ml and that of the control group was 308 +/- 59 units/ml; and the difference was significant (p = 0.000). With multivariate analysis, lymph node status (p = 0.000), distant metastasis status (p = 0.000) and maximum tumor diameter (p = 0.000) appeared as independent factors in regards to the significantly, higher serum concentrations of soluble interleukin-2 receptor. CONCLUSIONS Based on our preliminary results, the preoperative serum-soluble interleukin-2 receptor concentration is closely related to lymph node status, distant metastasis status and tumor diameter in invasive breast carcinoma. This may be an additional valuable predictive factor for the diagnosis of invasive breast cancer.