Evaluation of PIK3CA mutational status: a route towards a tailored diagnostic approach.

Evaluate the effectiveness and concordance of molecular methods in identifying mutations affecting the PIK3CA gene both on paraffin tissue sections of the tumor and on liquid biopsy of patients with breast cancer treated at the IEO. The molecular test on the liquid biopsy of same patient could bring an important benefit considering that the withdrawal of this biomaterial turns out to be less invasive than a biopsy performed on an organ

Inclusion Criteria:

• Participant has a histologically and/or cytologically confirmed diagnosis of ER+ and/or PgR+ breast cancer by local laboratory.
• Participant has HER2-negative breast cancer defined as a negative in situ hybridization test or an IHC status of 0, 1+ or 2+. If IHC is 2+, a negative in situ hybridization (Fluorescent in situ hybridization (FISH), Chromogenic in situ hybridization (CISH), or Silver-enhanced in situ hybridization (SISH)) test is required by local laboratory testing.
• Participants should be at advanced or metastatic setting prior to treatment.
• Written informed consent must be signed and dated by the patient and the investigator prior to inclusion.
• Patients must be accessible for follow-up.

Exclusion Criteria:

• patients already treated with different treatments like chemotherapy, hormone therapy etc

A total of n=100 PIK3CA-mutant HR+/HER2- metastatic breast cancer patients will be prospectively collected. The mutational status of PIK3CA will be assessed on patients' FFPE metastasis sample tissues using a NGS panel, which covers the entire length of PIK3CA (full gene coverage). Patients with mutant PIK3CA status will be involved in the study and their FFPE as well as plasma samples will be profiled with all the different techniques (one remaining NGS panel and 2 RT-PCR assays).