NOvel Immunotherapy Strategies for Advanced Triple Negative Breast Cancer (TNBC) Patients: TONIC-3 Trial

Inclusion Criteria: * Metastatic or incurable locally advanced triple negative breast cancer with confirmation of Estrogen receptor (ER) and Human Epidermal growth factor Receptor 2 (HER2) negativity (ER \<10%, HER2 IHC 0, 1+ or 2+ with no amplification) on a histological biopsy of a metastatic lesion * Patients with PD-L1 negative disease determined using the Combined Positivity Score (CPS\<10) (Dako 22C3 IHC) OR previously treated with anti-PD(L)1 in the (neo)adjuvant or metastatic setting (irrespective of PD-L1 status). * Metastatic lesion accessible for histological biopsy * 18 years or older * World Health Organisation (WHO) performance status of 0 or 1 * Maximum of three lines of chemotherapy, including antibody-drug conjugates and Poly-ADP Ribose Polymerase (PARP)-inhibitors, for metastatic disease and with evidence of progression of disease * Measurable or evaluable disease according to RECIST1.1 * Disease Free Interval (defined as time between first diagnosis or locoregional recurrence and first metastasis) longer than 1 year. This does not apply to patients with de novo metastatic disease or patients who did not receive (neo)adjuvant chemotherapy. * Adequate bone marrow, kidney and liver function Exclusion Criteria: * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris * Symptomatic brain metastases (subjects with asymptomatic brain metastases are eligible if these are free of progression for at least 4 weeks) * History of leptomeningeal disease localization * History of having received other anticancer therapies within 2 weeks of start of the study drug * History of severe allergic anaphylactic reactions to chimeric or humanized antibodies or fusion proteins * Known hypersensitivy to Chinese hamster ovary cell products or to any component of the atezolizumab or tiragolumab formulation * History of immunodeficiency, autoimmune disease, conditions requiring immunosuppression (\>10 mg daily prednisone equivalents) or chronic infections. * Prior treatment with an anti-CTLA4 or anti-TIGIT antibody. * Administration of live vaccine within 30 days of planned start of study therapy. * Active other cancer * Positive test for hepatitis B, hepatitis C, HIV and/or Epstein Barr virus (EBV) * History of uncontrolled serious medical or psychiatric illness * Current pregnancy pregnancy or breastfeeding.