Patients with low and intermediate grade tumors showing high AGR3 expression had an unfavorable outcome (mean tumor-specific survival: 142.5 ± 9.6 months; 95%CI: 123.8–161.2) compared with those with low AGR3 expression (mean tumor-specific survival: 181.7 ± 10.1 months; 95%CI: 162.0–201.4).The Cox regression model confirmed AGR3 to be a putative independent marker of unfavorable prognosis in low- and intermediate-grade breast tumors (multivariate HR: 2.186; 95%CI: 1.008–4.740;p < 0.05). This evidence concerns the gene AGR3 and breast neoplasm.