Abstract P2-10-10: Oncotype Dx testing in patients with synchronous unilateral primary breast cancer
Authors: Clark M , Coggan J , Dignam J , Rao R , Usha L , Kabaker K , Cobleigh M 
Published: February 2018

Introduction: Oncotype DX, is a commercial diagnostic test that is used to predict the likely benefit from chemotherapy in ER+, HER2-negative, node-negative breast cancer. Patients with multiple, synchronous ipsilateral primary breast cancers often have &gt;1 tumor tested if results from the first tumor show low or intermediate recurrence scores. Whether this approach is cost effective is unknown.

Methods: We reviewed Oncotype Dx results for 907 ER+/HER2- breast cancer patients seen at Rush University Medical Center from 2/2006 to 10/2016. Thirty-nine patients (35 with the same histology) had multiple, synchronous unilateral tumor samples tested. Results were reported both on the numeric risk score associated with the test and the categorized result (low/intermediate/high) recurrence risk. For patients undergoing more than 2 tests, the first two were arbitrarily chosen for the paired analysis. Descriptive statistics were used to examine the risk score distributions and assess potential correlation between paired samples. Statistical inference methods included estimating the correlation coefficient, regression models predicting one score with another, and evaluating the paired score differences with respect to mean deviation from zero. For categorized risk score, analysis evaluating category concordance between tumors was used to assess the degree of agreement. Analyses were conducted on all patients, and a subset consisting of patients whose two tumors had the same histology, where scores may be expected to exhibit greater concordance.

Results:Categorical risk score (RS): The concordance rate for risk category was 77% (30/39 patients) and Kendall's tau measure of association = 0.57, and was further increased to 80% (28/35 patients) and tau 0.63 for tumors with the same histology. Only one patient had tumor samples with low and high RS. A second patient had tumor samples with intermediate and high RS. Continuous RS: The correlation was 0.81 (p &lt; 0.0001). For tumors with the same histology, correlation increased to 0.83, with regression r2 (predicting second tumor RS value with first) = 0.69, indicating that the majority of variation in second score can be explained by variation in first score.

Conclusion: Oncotype Dx testing in patients with synchronous, unilateral primary breast cancers generally results in concordant results, even more so when the tumor samples are of the same histology. In our study, only 1 of the 39 patients had discordant low/high tumor pairs. Continuous scale tumor RS scores were highly correlated (&gt; 0.8). Therefore the benefit of testing additional samples appears marginal and, with the $4,620 cost per test, may not be cost-effective.

Citation Format: Clark M, Coggan J, Dignam J, Rao R, Usha L, Kabaker K, Cobleigh M. Oncotype Dx testing in patients with synchronous unilateral primary breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-10-10.