An estimation model for Oncotype Dx score using routine clinical and pathological parameters.
548 Background: Oncotype Dx(ODX) prognosticates the risk of recurrence and predicts the benefit of adjuvant chemotherapy in estrogen-receptor-positive breast cancer (BC). However, its cost makes it prohibitive for many health care systems. Our objective is to develop a model using routine clinical and pathological parameters to estimate ODX high risk category to guide adjuvant chemotherapy decisions. Methods: We retrospectively reviewed ODX and pathology reports from 190 early BC patients (2014 to 2016) in a specialized cancer center. Variables were selected through a multiple linear regression model. Coefficients of statistically significant variables were used to build an equation. Its results were divided into 2 estimated risk categories. ODX RS was also divided into 2 categories; above or below 25 (cut-off in TAILORx and RxPONDER). The final locked model was independently validated in 57 patients. Results: Among the tested variables, tumor size (pT), progesterone receptor (PR), Ki67 and Elston-Ellis grade were significantly associated with ODX RS (Table 1). The linear predictor is: (0.2544 x pT) – (0.0739 x PR) + (0.0861 x Ki67) + (5.4232 x Elston grade). The threshold score for this equation was set on 13 (median value) to discriminate low and high estimated risks. The correct classification rate (CCR) for the training and validation sets was 60% and 56%, respectively. CCR for high risk was 72% and 87% in the training and validation sets, respectively. Conclusions: An equation based on readily available variables correctly classified more than half of cases. Although the overall CCR is modest, our equation is remarkably useful for high risk cases requiring chemotherapy. With further validation, our model could provide a clinically useful estimation of high risk at lower cost. [Table: see text]