Optimization of surgical management of the axilla since MonarchE trial.

e12604 Background: Results of monarchE trial (1) have changed adjuvant therapy recommendations for estrogen-receptor-positive (ER+), HER-2 non amplified early breast cancer. Abemaciclib when combined with endocrine therapy has demonstrated a significant improvement in interval disease free survival for patients at high risk of recurrence defined by 4 or more positive nodes or 1 to 3 nodes and either tumor size ≥ 5cm or histologic grade 3. Given the importance of the extent of nodal disease in this study, surgical management of the axilla has resurfaced as a question asked at multidisciplinary tumor boards. Methods: Using data from a prospective historical cohort (2) in which patients underwent both sentinel node (SN) dissection and axillary node dissection (ALND), we assessed the proportion of patients in whom the absence of ALND indication would have led to a lack of awareness of "high-risk" status, and therefore of the indication for adjuvant Abemaciclib. In addition, we evaluated the contribution of the Katz nomogram (that predict pN2/N3 stage) (3) to guide possible indications for complementary ALND in patients with no indication for ALND according to current guidelines. Results: Among the 536 patients, 88 were excluded (54 were ER- and 34 had isolated cells in SLN). Among the remaining 448, 19.2% (86) already had an indication for abemaciclib (78 grade 3 and 8 with size ≥5cm). Ten patients with 3 SLN+ had an indication for ALND. Overall, among patients with 1 or 2 SLN+, only 8% (28/352) were pN2/N3 (14/279 with 1SLN+ and 14/73 with 2SLN+). When the ratio (number of SLN+/total number of SLN sampled) was less than 1, only 3.9% (9/231) were pN2/N3. The pN2/N3 rate was 16% (19/121) when the ratio was greater than 1. Patients with 1 or 2 SLN + met the ACOSOG Z0011 criteria so none would benefit from an ALND, but 8% (28/352) of patients at high risk will not receive Abemaciclib. When using the Katz nomogram with a threshold ≤5%, this rate decreases to 3.3% (7/352) but 116 patients will have an ALND with no benefit. With a threshold ≤20%, 5% (16/352) patients at high risk will not receive Abemaciclib but 21 patients will have an ALND with no benefit. Conclusions: The indications for adjuvant abemaciclib should not lead to surgical escalation in the surgical management of the axilla. 1.Johnston SRD et al. Lancet Oncology. 2023. 2. Katz A et al. J Clin Oncol. 2008 3. Werkoff G et al. J Clin Oncol. 2009.