Ki 67 is a major, but not the sole determinant of Oncotype Dx recurrence score.

Background: Immunohistological assessment of Ki 67 expression is less expensive than Oncotype Dx, which is currently used to identify patients with lymph node-negative breast cancer, who will benefit from adjuvant chemotherapy.

Methods: The relationship of immunohistologically measured Ki 67 to Oncotype DX recurrence score (RS) was examined in 53 cases of T1-2 N0 M0 (oestrogen receptor-positive, HER2/neu negative) breast cancer.

Results: There was a strong linear correlation between Ki 67 value and the Oncotype Dx RS. All patients in the low Ki 67 group (Ki 67 of ≤ 10%) had Oncotype Dx RSs of low or intermediate risk. The vast majority of patients (93.8%) in the high-Ki 67 group (Ki 67 ≥ 25%) had oncotype RSs of high or intermediate risk.

Conclusion: Ki 67 proliferation value is a major, but not the sole determinant of Oncotype Dx score.