Neo-adjuvant Chemotherapy Combined With Stereotactic Body Radiotherapy to the Primary Tumour +/- Durvalumab, +/- Oleclumab in Luminal B Breast Cancer:

Neo-CheckRay is a multicenter, open-label phase II study that randomizes luminal B breast cancer subjects candidate for neo-adjuvant chemotherapy in a 1:1:1 ratio in 3 arms: 1. the combination of weekly paclitaxel followed by dose-dense doxorubicin-cyclophosphamide (ddAC) and pre-operative radiation therapy (boost dose) on the primary tumour 2. arm 1 with the addition of the anti-PD-L1 antibody durvalumab 3. arm 2 with the addition of the anti-CD73 antibody oleclumab The primary tumour will be excised 2-6 weeks after completion of ddAC. A safety run-in is planned for the 6 first subjects before starting the randomized phase II trial. Those 6 subjects will receive the treatment given in Arm 3.

Inclusion Criteria: * Age ≥ 18 years old * Female * ECOG performance status ≤ 1 * Weight ≥ 35 kg * Histological diagnosis of invasive breast adenocarcinoma that is estrogen receptor-positive (ER-positive) and HER2- negative, as per the updated American Society of Clinical Oncology (ASCO) - College of American Pathologists (CAP) guidelines and performed according to local testing. In addition, only tumours with Proliferation Index Ki67 ≥ 15% or histology grade III are accepted. * Agreement to perform new study related biopsies to provide tissue samples * MammaPrint genomic high risk score according to centralised testing, except for specific conditions as mentioned below. Mammaprint will only be tested for luminal B breast tumours with either Proliferation Index Ki67 ≥ 15% or histology grade III tumours. (Testing to be done during screening period). MammaPrint result status at time of termination of all other screening procedures * MammaPrint is high risk: subject may be randomized. * MammaPrint is low risk: subjet can not be randomized. * MammaPrint result is not yet known: If the MammaPrint result is not known at time of termination of all other screening procedures, the investigator is allowed to randomize the subject and start study treatment without waiting for the result of the MammaPrint in the following situations: (Ki67 \> 20 % or grade III) and Age\