SEQUEL-Breast

The most important inclusion criteria are:

1. Adult women (≥ 18 years of age) and men with proven diagnosis of adenocarcinoma of the breast with locoregional recurrent or metastatic disease not amenable to resection or radiation therapy with curative intent and for whom chemotherapy is not clinically indicated.
2. Documentation of histologically or cytologically confirmed diagnosis of estrogen receptor (ER) expression >10% and/or progesterone receptor (PR) expression >10% breast cancer based on local laboratory results. In case ER ≤ 10% and PR >10% the ER and PR expression need to be confirmed in a referral center. Tumor must be HER2-negative as defined by ASCO-CAP guidelines. If HER2 status is unavailable then testing must be performed/repeated.
3. Patients must have progressed on fulvestrant as a preceding treatment line (as first or second line therapy). In case fulvestrant plus a CDK4/6 inhibitor has been given in 1st line as last treatment, the patient must have progressed during or shortly (<12 months) after stopping adjuvant treatment with an (NS)AI.
4. Previous treatment with a CDK4/6 inhibitor in the advanced setting is mandatory.
5. The presence of an activating PIK3CA mutation; preferably detected in a metastasis as PIK3CA mutation status may change during the course of the disease. In case a biopsy from a metastasis is not obtainable, mutation analysis may be performed on the primary tumor or archival tumor material.
6. Evaluable disease* as defined per RECIST v.1.1. Tumor lesions previously irradiated or subjected to other locoregional therapy will only be deemed measurable if disease progression at the treated site after completion of therapy is clearly documented.*Evaluable disease in this study is defined as measurable and non-measurable disease according to RECIST, with the exception of truly non-measurable disease only (i.e. ascites or pleural effusion as only site of disease). In case of truly non-measurable disease only, a patient is NOT considered evaluable according to RECIST. Bone only disease is considered evaluable.