A Study of Atezolizumab and Paclitaxel Versus Placebo and Paclitaxel in Participants With Previously Untreated Locally Advanced or Metastatic Triple Negative Breast Cancer (TNBC)

Inclusion Criteria: * Participants with locally advanced or metastatic, histologically documented TNBC (absence of human epidermal growth factor receptor 2 \[HER2\], estrogen receptor \[ER\], and progesterone receptor \[PR\] expression), not amenable to surgical therapy * Participants eligible for taxane monotherapy * No prior chemotherapy or targeted systemic therapy (including endocrine therapy) for inoperable locally advanced or metastatic TNBC * Availability of formalin-fixed paraffin-embedded (FFPE) tumor block (preferred) or at least 17 unstained slides, collected ≤3 months prior to randomization, with an associated pathology report, if available. If a tumour sample taken within 3 months before randomisation is not available and a tumour biopsy is not clinically feasible, the primary surgical resection sample or the most recent FFPE tumour biopsy sample may be used. Of these additional options, the most recent sample should be used. * Eastern Cooperative Oncology Group performance status of 0 or 1 * Life expectancy at least 12 weeks * Measurable disease, as defined by RECIST v1.1 * Adequate hematologic and end-organ function * Negative human immunodeficiency virus (HIV) test at screening. * Negative hepatitis B surface antigen (HBsAg) test at screening * Negative total hepatitis B core antibody (HBcAb) test at screening, or positive HBcAb test followed by a negative hepatitis B virus (HBV) DNA test at screening. The HBV DNA test will be performed only for patients who …