Abstract 265P
Background
Inflammatory breast cancer (IBC) is an aggressive BC subtype with rapid onset and poor outcomes. After biopsy confirmation, first-line treatment is based on systemic chemotherapy. A targetable somatic PIK3CA mutation is reported in 30% of IBC, allowing for treatment by PI3Kα-specific inhibitors, such as alpelisib. The aim of this study was to evaluate the detection rate of circulating PIK3CA mutation in non-metastatic IBC patients harbouring a PIK3CA mutation on initial biopsy.
Methods
This monocentric retrospective study was based on available stored plasmas and biopsies at diagnosis and included all non-metastatic IBC patients who were treated by neo-adjuvant chemotherapy. PIK3CA mutations (E542K, E545K, H1047R/L) were assessed by droplet digital PCR (ddPCR) in plasma samples and tumoral tissue at diagnosis.
Results
A total of 54 patients treated between 2008 and 2018 in Henri Becquerel Center and with sufficient DNA from tumor tissue were included. 14/54 patients (26%) had a PIK3CA mutation identified on baseline biopsy (H1047R=8; H1047L=3; E545K=2; E542K=1). All mutations were single. Among them, 11 (76%) patients had enough circulating DNA for circulating mutations analyses. Corresponding circulating PIK3CA mutations were found in 4/11 patients (36%). Beside these 4 patients, no other circulating mutation was identified among the 42 patients with fully interpretable circulating and biopsy mutational analyses.
Conclusions
Our results showed that corresponding circulating PIK3CA mutation was identified in 36% of non-metastatic IBC patients with baseline somatic PIK3CA mutation on tumor tissue while no circulating mutation was found among non-mutated PIK3CA patients. Further studies are needed to determine the prognostic and therapeutic impact of circulating PIK3CA mutation in IBC patients.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Henri Becquerel Center.
Funding
Henri Becquerel Center La Ligue Contre le Cancer.
Disclosure
M. Fontanilles: Travel/Accommodation/Expenses: F. Hoffmann–La Roche; Travel/Accommodation/Expenses: GSK. F. Di Fiore: Honoraria (self): Roche; Honoraria (self): Amgen; Honoraria (self): Merck; Honoraria (self): Sanofi; Honoraria (self): Bayer; Honoraria (self): Servier; Honoraria (self): Janssen. F. Clatot: Honoraria (self), Travel/Accommodation/Expenses: BMS; Honoraria (self), Travel/Accommodation/Expenses: Lilly; Honoraria (self), Travel/Accommodation/Expenses: Merck; Honoraria (self), Research grant/Funding (institution), Travel/Accommodation/Expenses: Roche; Research grant/Funding (institution): AstraZeneca. All other authors have declared no conflicts of interest.