Abstract P4-14-05: Confirmation of the TAILORx 21-gene expression trial using a real world observational database

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Abstract Background: The TAILORx study (NCT00310180)(TRx) has demonstrated the efficacy of endocrine therapy alone in early stage, lymph node negative, hormone receptor positive, her2neu oncogene negative breast cancer harboring an intermediate recurrence score (RS) on a 21-gene profile (OncotypeDx), obviating the need for adjuvant chemotherapy in a large subset of women. The study randomized and followed 6711 patients (pts) and required 9 years to reach its conclusion endpoints. The availability of the electronic health record (EHR) permits automated reviews, facilitating more rapid “real world” hypothesis testing (but not a replacement for randomized clinical trials), especially when there are clear variations in common practice patterns. However physician bias in treatment selection needs to be considered. Methods: A retrospective review of the Cota Observational Cancer database, drawn from EHRs, of female pts with breast cancer who were 18 to 75 years of age; had hormone-receptor–positive, human epidermal growth factor receptor 2 (HER2)–negative, axillary node–negative breast cancer harboring an OncotypeDx RS 11-25 receiving adjuvant therapy following surgical resection of a 11-50 mm primary tumor (similar to TRx eligibility). Results: 1009 pts from 23 cancer centers (107 oncologists) were identified, 850 (84.2%) received adjuvant endocrine therapy alone (E) and 159 (15.8%) received adjuvant chemoendocrine therapy (CE) as part of standard care (no randomization). 285 pts were age <50 yrs (E:218, CE:67) and 601 pts has RS 16-25 (E:453, CE:148). Treatment selection was imbalanced with oncologists more likely to utilize CE in younger pts (median age E: 59 yrs, CE: 53 yrs; p<0.01), larger tumors (median tumor size E: 16mm, CE: 20mm; p<0.001) and higher RS (median RS E: 16, CE: 21; p<0.001). With a median follow-up for survival since diagnosis of 3.7 years, the Kaplan-Meier estimated 5 yr overall survival rates were 98.9% with E and 97.8% with CE (p=0.23); the corresponding 5-yr OS in TRx were E: 98% and C: 98.1%. With a median 1.7 years follow-up for recurrence, 19 pts have suffered a disease distant or local recurrence (E: 13, CE: 6) yielding a 5-year recurrence-free survival of E: 95.2% and CE: 91% (p=0.05); the corresponding TRx result was E: 96.9% and CE: 97%. The 5-yr invasive disease-free survival (IDFS = death, local/distant, second primary) with 32 events was E: 92.7% and CE: 81.9% (p= 0.05); corresponding TRx E: 92.8 % and CE: 93.1%. Given the imbalance in treatment allocations, a multivariate analysis was performed, with older age (<0.001), CE choice (<0.006) and larger tumor size (p<0.05) remaining significant, but not increased RS (p=0.16) for 5-year IDFS. Among women age <50 with RS 16-25 (E: 118; CE: 60) the 5-yr IDFS was E: 95% and CE: 94%; the corresponding RS 16-20 TRx E: 92% and CE: 94.7% and RS 21-25 E: 86.3% and CE: 92.1%. Conclusions: Using a real world data source, endocrine therapy alone appears to yield excellent 5-yr survival rates among pts with 21-gene RS 11-25 similar to the TAILORx trial. Treatment selection bias (with perceived higher risk pts allocated to CE) and shorter median follow-up limits full confirmation by this dataset. Citation Format: Waintraub SE, Isaacs C, Norden AD, Graham DA, McNamara DM, O'Neill SC, Lakshmanan A, Wu T, Maresca A, Pecora AL, Goy AH, Goldberg SL. Confirmation of the TAILORx 21-gene expression trial using a real world observational database [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-14-05.