Correlating Ki67 and other prognostic markers with oncotype DX recurrence score in early breast cancer

Background: Breast cancer is a common problem. Decisions regarding adjuvant chemotherapy are complex. Ki67 is increasingly used, in conjunction with conventional prognostic markers, to help decide the use of adjuvant chemotherapy for early breast cancer. Ki67 may be an economical alternative to Oncotype DX recurrence score (RS), which is a validated prognostic marker for disease recurrence and predictive marker for benefit from chemotherapy. Methods: We reviewed all cases of luminal type early breast cancer (T1–2, N0–1mi, M0, ER positive, HER2 negative) referred for Oncotype DX testing (n = 58) at an Australian tertiary private hospital from 14 December 2006 to 31 December 2013. RS was correlated with Ki67, along with other conventional prognostic markers including tumour size, grade, mitotic rate and lymphovascular invasion. Spearman's rank order correlation coefficient and Pearson product-moment correlation coefficient (r) were used for ordinal and continuous variables respectively. Results: The median Ki67 was 15% (range 2–50), the median RS was 16 (range 3–65). There was no positive correlation between Ki67 and RS (r = 0.012, P = 0.929). No single conventional prognostic marker was shown to significantly correlate with RS, including tumour size (r = −0.021, P = 0.878), grade (r = 0.103, P = 0.442), mitotic rate (r = −0.072, P = 0.692) and lymphovascular invasion (r = −0.124, P = 0.385). Conclusions: Ki67 and conventional prognostic markers do not correlate with Oncotype DX recurrence score. In the setting where conventional prognostic markers do not show a clear indication for or against adjuvant chemotherapy, Ki67 is not a substitute for Oncotype DX testing.