The impact of the 21 gene recurrence score (RS) on chemotherapy prescribing in estrogen receptor positive (ER plus ), lymph node positive (LN plus ) breast cancer (BC) in Ireland: A national, multi-centre, prospective study

Background: The 21 gene recurrence score (OncotypeDx ®) is reimbursed in Ireland to guide adjuvant treatment decisions for ER+, LN-negative, human epidermal growth factor receptor 2 (HER2)-negative BC. There is emerging evidence supporting the clinical utility of this test in patients with LN+ disease. Although the exact cut-off for chemotherapy has not been defined in this population, SEER data support the omission of chemotherapy for patients with RS Results: In total, 294 patients were enrolled across the - nine centres. Complete data is available on 123 patients (range 38 to 75, median 54 years), which included two male patients. Of the remaining 121 (98%) patients, 49 (40%) were premenopausal, 26 (21%) perimenopausal and 46 (37%) postmenopausal. The median tumour size was 38 mm (Range 7 to 58 mm). There were 101 (82%) patients with invasive ductal carcinoma, 17 (14%) with lobular carcinoma and 5 (4%) classified as other breast histology. Seventeen patients (14%) had grade 1, 74 (60%) grade 2 and 32 (26%) grade 3 disease. There were 79 (64%) patients with 1 LN+, 35 (29%) with 2 LN+ and 9 (7%) with 3 LN+ status. Overall access to the 21 gene RS test led to a 32% reduction in chemotherapy, 112 (91%) to 72 (59%) patients. This was most notable in patients with ductal histology (91 vs 61) and grade 2 breast cancer (66 vs 41) representing a 24.4% and 20.3% reduction, respectively. Similarly patients with 1 LN+ (71 vs 46) and 2 LN+ (34 vs 21) represented a 20.3% and 9.7% reduction, respectively. This study also identified four patients aged less than 40, for whom chemotherapy was not recommended. The biggest reduction in chemotherapy occurred in women aged over 50 (62 vs 36) at 21.1%. Overall, in 65% of cases, medical oncologists deemed the RS test result significantly changed treatment recommendations. Conclusion: These findings are consistent with results from similar studies in other countries. Broader access to the 21-gene RS could result in a reduction in the use of chemotherapy in Ireland. Citation Format: William J Mullally, Dara Bracken-Clarke, Andrew Padmore, Seamus O9Reilly, Deirdre O’Mahony, Janice Walshe, John Kennedy, Rajnish Gupta, Cathy Kelly, Miriam O9Connor, Karen Duffy, Maccon Keane, Bryan T Hennessy, Patrick G Morris. The impact of the 21 gene recurrence score (RS) on chemotherapy prescribing in estrogen receptor positive (ER+), lymph node positive (LN+) breast cancer (BC) in Ireland: A national, multi-centre, prospective study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-56.