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495P Prognostic value of PIK3CA mutational status in tissue & plasma in HR+/HER2- breast cancer (BC)

2023; Elsevier BV; Volume: 34; Linguagem: Inglês

10.1016/j.annonc.2023.09.1080

1569-8041

R. Lozano Mejorada, E. Terán Brage, J.A. Muñoz León, Á. López Gutiérrez, Luis Figuero-Pérez, A. Rodrígues Francoso, R. Seijas Tamayo, D. Morchón Araujo, M.D.C. Garijo Martínez, Jonnathan Roldán Ruíz, Manuel Miralles Hernández, M. Salas, E. Fonseca Sánchez, César Augusto Rodríguez Sánchez,

Cancer Treatment and Pharmacology

PIK3CA mutations are described in about 30-40% of BC. They confer resistance to endocrine therapy and overall worse prognosis. Concordance between testing methods (tissue & plasma) are not widely studied. We aim to correlate tissue & plasma assays and to analyze the prognostic value of PIK3CA mutations in HR+/HER2- BC. Retrospective and unicentric analysis of PIK3CA mutational status in tissue & plasma samples in patients (p) with HR+/HER2- BC from Feb/21 to Mar/23. PIK3CA test: Cobas®PIK3CA Mutation Kit. We correlated both diagnostic methods and analysed progression-free survival (PFS) in PIK3CA mutated (PIK3CAm) vs wild-type (wt). We analyzed 225 samples in 161p with HR+/HER2- BC (149 in tissue & 76 in plasma). PIK3CA mutations were detected in 62p (38.5%), of which 39.6% (59p) in tissue and 11.8% (9p) in plasma. Hotspot mutations: H1047X (45.7%), E545X (20%) and E542K (12.8%). Tissue & plasma correlation was conducted in 64p (M1 stage), with overall correlation rate of 70.3%. 19 cases (29.7%) were positive in tissue but not in plasma. 80p received treatment with CDK4/6 inhibitors + endocrine therapy. PFS was shorter in PIK3CAm vs wt (24m vs 30m; HR=1.39 [95%CI,0.7-2.4], p=0.25). A sub-analysis was performed based on exons 9 & 20, showing a significantly lower PFS in PIK3CAm exon 9 vs 20 population (9.7m vs 30.3m; HR=2.84 [95%CI,1.1-7.4], p=0.02). Although we observed a poorer PFS in p with visceral involvement in PIK3CAm (21.9m vs 30.1m; HR=2.82 [95%CI,0.6-12.3], p=0.14), in a multivariate analysis, mutations in exon 9 were an independent poor prognostic factor regardless visceral involvement; p=0.027.Table: 495PTissueMutatedWild-typeTotalPlasmaMutated9 (32.1%)0 (0%)9 (14.1%)Wild-type19 (67.8%)36 (100%)55 (85.9%)Total28 (100%)36 (100%)64 (100%)Positive agreement: 9/28 (32.1%)Negative agreement: 36/36 (100%)Overall agreement: 45/64 (70.3%) Open table in a new tab Our results support the determination of PIK3CA in tissue as the diagnostic method of choice, although further studies are needed to assess the role of liquid biopsy in the detection of PIK3CAm. In our population, the presence of PIK3CAm confers worse prognosis in luminal BC, being significantly worse in mutation carriers in exon 9 regardless visceral involvement.