[192] Validation of the Magee Study Equation in Prediction of Breast Cancer Recurrence Risk Category by Oncotype DX™

NN Esposito, G Acs, DJ Dabbs, M Flanagan, C Laronga, R Bhargava. H. Lee Moffitt Cancer Center, University of South Florida, Tampa; Magee-Womens Hospital of the University of Pittsburgh, Pittsburgh; H. Lee Moffitt Cancer Center, Tampa; University of West Virginia, Morgantown

Background: Oncotype DX™ is a commercially available RT-PCR-based assay that provides a Recurrence Score (RS) and has been shown to provide prognostic and predictive information in ER-positive lymph node-negative breast cancer. The RS is divided into 3 risk categories as low, intermediate and high risk of tumor recurrence at 10 years. It has been recently shown that the RS can also be estimated by traditional histopathologic variables in approximately 2/3rd of cases using the Magee study equation (MSE) RS =13.424 + 5.420 (nuclear grade) + 5.538 (mitotic count) - 0.045 (ER immunohistochemical score) - 0.030 (PR immunohistochemical score) + 9.486 (HER2/neu) (Mod Pathol 2008;21:1255-61).
Design: The histopathologic variables of 154 cases were scored by 2 pathologists (GA and NNE) blinded to Oncotype DX™ results. The MSE was used to determine the risk category in all cases. The risk category obtained by the equation and the Oncotype DX™ RS were then compared.
Results: The concordance between the risk categories based on Oncotype DX™ RS and the RS using the MSE was 72% (111/154). Of the 43 discordant cases, 42 showed 1-category discordance and one case had 2-category discordance. Among the discordant cases, the mean and median differences in RS by the MSE vs Oncotype DX™ were 4.13 and 6.15, respectively (range 0.7-18.1). Of the discordant cases, 55.8% of the cases had a <10 RS point difference. The risk category in 17/43 discordant cases (39.5%) was altered by a RS margin of <2.

Comparison of risk categories using the Magee Study Equation vs. Oncotype Dx

	High risk using MSE†	Intermediate risk using MSE†	Low risk using MSE†	Total
High risk on ODX*	9	5	0	14
Intermediate risk on ODX*	2	18	25	45
Low risk on ODX*	1	10	84	95
Total	12	33	109	154

*ODX=Oncotype DX™, †=Magee study equation


Conclusions: This is the first study to independently validate the Magee study equation. This validation study confirms that the Oncotype DX™ RS is heavily influenced by the level of tumor hormone receptor expression, proliferation rate, nuclear pleomorphism, and HER2 status. Traditional histopathologic variables can thus be judiciously utilized in treatment decisions and Oncotype DX™ testing should be reserved for more complicated cases only.
Category: Breast

Wednesday, March 24, 2010 9:30 AM

Poster Session V # 26, Wednesday Morning