Discordance between oncotype DX recurrence score and RSPC for predicting residual risk of recurrence in ER-positive breast cancer

Oncotype DX, a gene expression assay widely employed to aid decision making on adjuvant chemotherapy use in patients with primary oestrogen receptor-positive (ER+) breast cancer, produces a recurrence score (RS) related to distant disease recurrence (DR) risk (RS%). In node-negative patients, RS can be integrated with clinicopathological parameters to derive RS-pathology-clinical (RSPC) that improves prognostic accuracy. Data were collected on patients having clinically indicated tests with an intermediate clinical risk of distant recurrence, and for whom the decision to prescribe chemotherapy remained unclear. Correlation between RS% and RSPC scores was examined. An agreement table was constructed using risk-categorised data. Association between RS%-derived categorical risk assignments and treatment recommendation was evaluated. Data on 171 tests (168 patients) were available. Median DR risk by RS% was 11% (range 3-34%), by RSPC it was 15% (range 4-63%). Correlation between RS% and RSPC was 0.702 (p < 0.001). RS% classified 57.3% of cases as low-, 32.2% intermediate- and 10.5% high-risk for DR; by RSPC proportions were 33.9, 35.7, and 30.4%, respectively. The number of patients receiving chemotherapy recommendations was: 14/87 (16.1%) categorised as low-risk by RS%, 27/49 (55.1%) as intermediate-risk and 12/13 (92.3%) as high-risk. Of 149 patients recommended for endocrine treatment alone, 28 (18.8%) were categorised by RS% as low-risk but by RSPC as intermediate- or high-risk. In this group of patients, RSPC assessed fewer patients as low-risk and more as high-risk than did RS%. The discordances between the scores indicate that RSPC estimates of risk should be considered when selecting patients for endocrine therapy alone.