Comparison of risk categories defined by Ki-67 and the EndoPredict test in luminal-type breast cancer

Aim:

Ki-67 can be helpful in decision making for or against chemotherapy in patients with hormone receptor (HR) positive, HER2 negative breast cancer. However, the multigene assay EndoPredict (EP) has shown to be able to provide additional information on the well-established pathological factors regarding the estimation of the risk of recurrence. In this study, we evaluated the relevance of Ki-67 for risk categorization in the framework of EP test results.

Material:

We compared prospective EP test results (n = 373) with data on the proliferation index assessed by Ki-67 immunohistochemistry in HR positive, HER2 negative breast cancer. We statistically investigated the association of both parameters to compare risk categorizations.

Results:

EP testing resulted in 172 low and 201 high EPscores. The combination of EPscore with the pathological tumor stage and nodal status resulted in 238 EPclin low risk and 135 EPclin high risk cases. Both scores were significantly associated with Ki-67 (p < 0.001). However, EPscore high and EPclin score high-risk were found in carcinomas with low Ki-67, and vice versa. Low Ki-67 levels (≤10%) were observed in 10% of the EPscore high group and in 13.5% of the EPclin high-risk group. In contrast, only 5.7% of EPscore low tumors had high Ki-67 levels (≥25%).

Conclusions:

Ki-67 shows an association with the EPscore and EPclin score. Ki-67 values above 25% have a large overlap with the EP high risk categories. However, low and intermediate Ki-67 values (< 25%) alone were not reliable parameters for predicting a low risk EP or EPclin result.