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BACKGROUND: Although no survival benefit has been demonstrated by treating early breast cancer (BC) with neoadjuvant chemotherapy (NAC), it is now widely accepted as first intention strategy in triple negative and HER2-positive BC. However, the benefit of the neoadjuvant strategy is controversial in luminal tumours. The latter are considered as poor responder to chemotherapy and it remains unknown if delaying time to surgery by providing NAC as first treatment might be deleterious. The aim of this study was to compare the prognosis of patients with Luminal B BC treated with either NAC, either adjuvant chemotherapy. MATERIALS AND METHODS: We retrospectively identified in our institutional database 188 patients with grade 3 luminal B BC treated with NAC and 1203 patients treated with the same adjuvant chemotherapy (AC). To deal with the selection bias, the contribution of each subject was weighted by a propensity score (PS): 1/PS for patient with the NAC strategy and 1/(1-PS) for patients with the AC strategy. This enables to generate a pseudo-population with a balanced covariates combination between groups. We evaluated the disease free survival (DFS), the distant metastasis free survival (DMFS) and the overall survival (OS) using a weighted Cox model. To analyse the effect of NAC in high-risk subgroups, we introduced in the model interaction effects with the initial tumour size and the initial clinical nodal status. RESULTS: By construction, patients, tumor characteristics and trastuzumab use were similar between the population treated with NAC and the population treated with adjuvant CT. After PS weighting and adjustment on confounding factors, DFS (HR = 2.56, 95%IC [1.73 - 3.78]; p< 0.001), DMFS (HR = 1.28, 95%IC [1 - 1.63]; p < 0.001) and OS were lower in the NAC group (HR = 1.51, 95%IC [1.10-2.09]]; p = 0.01) when compared with the group of patients treated with adjuvant chemotherapy.The interaction test between the initial clinical nodal status, initial clinical tumour size and survival endpoints was significant, highlighting a different prognostic effect of NAC versus AC in nodes-positive than in node-negative patients, and a different prognostic effect of NAC versus AC in small than in large tumours. No significant DFS nor OS difference was found in node-negative patients. In node-positive patients with tumour larger than 20mm, the risk of death was nearly doubled when comparing NAC strategy to AC strategy (HR=2.30, 95%CI [1.34-3.4]), while the highest deleterious impact on OS of the NAC strategy against the AC strategy was observed in node-positive patients with a tumour size smaller than ≤20mm (HR=3.52, 95%CI [1.59-7.8]). CONCLUSION: In node-positive, grade 3, luminal B tumours, receiving NAC seems associated with an impaired survival when compared with receiving the same treatment in the adjuvant setting. Our results suggest that surgery as first treatment could be the preferred option, even if breast-conserving surgery cannot be obtained. In tumors smaller than 20mm, NAC strategy should be avoided irrespective of the nodal status. Citation Format: Enora Laas, Thomas Gaillard, Jean Guillaume Feron, Jean-Yves Pierga, Florence Coussy, Beatriz Grandal, Audrey Bellesoeur, Eléonore De Guillebon, Sonia Rozette, Clemence Evrevin, Lucie Laot, Marick Lae, Anne Sophie Hamy, Fabien Reyal. Impact of neoadjuvant chemotherapy on survival in luminal B tumours: A propensity score weighted analysis [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 P2-16-35.

INTRODUCTION: Neoadjuvant chemotherapy (NAC) is increasingly being used for locally advanced breast cancers (BCs) or aggressive BC tumors. However, no survival benefit of the neoadjuvant approach over receiving chemotherapy in the adjuvant setting has been proven so far in HER2-positive early breast cancer (BC) patients. The objective of this study was to compare the prognosis of patients with an HER2-positive BC treated with NAC to patients treated with adjuvant chemotherapy (AC). MATERIALS AND METHODS: We retrospectively identified in our institutional database 203 patients with HER2-positive BCs treated with NAC plus trastuzumab and 701 patients treated with adjuvant chemotherapy. As the treatment was not randomly allocated, we used a propensity score with an Inverse probability of received treatment weighting (IPTW) to generate a pseudo-population in which each covariate combination was balanced between treatment groups. The disease free (DFS), distant metastasis free (DMFS) and overall survival (OS) were evaluated using a weighted Cox model. The interactions with poor prognosis factors (initial tumour size, tumour grade, hormone receptor status and initial clinical nodal status) were tested to evaluate the effect of the NAC in high-risk tumours. RESULTS: By construction, patients, tumor characteristics and trastuzumab use were similar between the population treated with NAC and the population treated with adjuvant CT. No difference was found regarding DFS (p=0.3) neither DMFS (p=0.4) in the global population. However, there was a significant interaction effect between the strategy and the initial clinical nodal status, with a DFS benefit of NAC over AC in the node-positive group (HR 0.53 CI95% [0.31- 0.89]), as well as for DMFS (HR 0.39 95%CI [0.20-0.77]). We found a significant benefit in OS with the neoadjuvant strategy when compared with the adjuvant strategy (HR = 0.12 95%CI [0.03-0.47], p=0.002) and this difference was significant irrespective of tumour size, initial clinical nodal status and hormone receptor status. CONCLUSION: In patients with HER2-positive BCs, receiving NAC is associated with an improved OS when compared with chemotherapy received in the adjuvant setting. Our results support the fact that NAC should become a standard of care in HER2-positive tumours. Citation Format: Enora Laas, Arnaud Bresset, Jean Guillaume Feron, Jean-Yves Pierga, Florence Coussy, Audrey Bellesoeur, Beatriz Grandal, Eléonore De Guillebon, Sonia Rozette, Clemence Evrevin, Thomas Gaillard, Marick Lae, Anne Sophie Hamy, Fabien Reyal. Survival benefit of neoadjuvant chemotherapy versus adjuvant chemotherapy in HER2-positive early breast cancer: A propensity score-weighted analysis [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 P2-16-36.