The impact of oncotype DX testing on adjuvant chemotherapy decision making in breast cancer with micrometastasis to the sentinel lymph node.

Introduction: Oncotype-DX testing has reduced adjuvant chemotherapy use in breast cancer but there is limited evidence on patients with sentinel lymph node micrometastasis (SLNmi). This study aimed to evaluate the real-world use of Oncotype-DX testing on adjuvant chemotherapy decision-making in patients with SLNmi.

Methods: This retrospective cohort analysis included ER-positive, HER2-negative patients with SLNmi treated during 2016-2022 at a tertiary care hospital. A three-member simulated multidisciplinary team (MDT) panel, who were blinded to the Oncotype recurrence score (RS), made chemotherapy recommendations using clinicopathological data and PREDICT scores. The simulated MDT recommendations were then compared with the Oncotype RS. RS≥26 was used to identify patients who would benefit from adjuvant chemotherapy.

Results: A total of 77 patients (median age 58 years) were included. Most (69%) patients underwent breast conservation. Most tumours (71%) were ductal, Grade 2 (68%); 39% had lymphovascular invasion. Median tumour size was 23mm. Median number of SLNs excised was 2; the median Oncotype RS was 16 (range 0-45). Six patients had RS≥26; all were recommended for chemotherapy by the simulated MDT. Of the 71 patients with RS ≤25, the simulated MDT recommended chemotherapy in 19 (27%), a personalised chemotherapy discussion in 35 (49%) and no chemotherapy in 17 (24%). Thus, 76% of these patients had a change in management with Oncotype-DX, avoiding a recommendation or a discussion regarding chemotherapy.

Conclusions: This real-world analysis found that Oncotype-DX aids adjuvant treatment decision making in patients with SLNmi, changing the recommendation to give chemotherapy in up to 76% of the cohort.