Circulating ESR1 mutation detection rate and early decrease under first line aromatase inhibitor and palbociclib in the PADA-1 trial

Congress : SABCS

Authors : Bidard F-C, Pistilli B, Dalenc F, De la Motte Rouge T, Sabatier R, Frenel J-S, Ladoire S, Dubot C, Ferrero J-M, Levy C, Lortholary A, Stefani L, Mouret-Reynier M-A, Hardy A-C, Jacquin J-P, Grenier J, Chakiba C, Teixeira L, Soulie P, Everhard S, Lemonnier J, Jeannot E, Bieche I, Berger F, Pierga J-Y, Bachelot T, Delaloge S.

Experts group or program : French Breast Cancer Intergroup (UCBG).

Palbociclib (Pal) combined with an aromatase inhibitor (AI) is a standard of care as first line therapy in ER+ HER2- metastatic breast cancer (MBC). While ESR1 mutations (ESR1mut) are a characterized mechanism of resistance to AI as single agent, it remains unknown how these mutations, when detected prior to treatment initiation, may affect the efficacy of Pal+AI. In a subsidiary analysis of the first line PADA-1 trial, we report the ESR1mut detection rate at baseline and, in patients with ESR1mut detected at baseline, how ESR1 circulating tumor DNA levels changed after the first cycle of AI-Pal therapy.

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