The prognostic significance, as well as the relationship with known prognostic factors in breast cancer, of insulin-like growth factor 1 receptor (IGF-1-R), epidermal growth factor receptor (EGF-R), and somatostatin receptor (SS-R) was evaluated. IGF-1-R was positively correlated with estrogen receptor and age, but not significantly with progesterone receptor, lymph node status, and tumor size. EGF-R was negatively correlated to estrogen receptor and progesterone receptor, whereas no association was found with age, lymph node status, and tumor size. The levels of the tumor contents of IGF-1-R and EGF-R were not significantly related to tumor recurrence in 214 patients (test for trend, P = 0.20 and P = 0.08, respectively). However, patients with tumors containing intermediate levels of EGF-R (0.5 to 2.0 fmol/mg of membrane protein) experienced a longer disease-free survival than did patients with tumors possessing lower or higher levels of EGF-R. This effect was most pronounced in the subgroup of patients with positive axillary lymph nodes: 66% disease-free after 5 yr compared with 38% and 46% for the groups with lower and higher EGF-R levels, respectively. The relapse-free survival for patients with tumors containing SS-R (15%) was significantly longer than for patients with SS-R-negative tumors (82% versus 46% disease free after 5 yr, P = 0.04). Assessment by multivariate analysis showed that lymph node status, tumor size, and differentiation grade were independent prognostic factors for relapse. In the Cox model, estrogen receptor and progesterone receptor were both negatively correlated with tumor recurrence, whereas overall EGF-R and IGF-1-R did not show such a relation.