Background: TNBC patients have poorer survival outcomes when compared to other types of breast cancer, due to the lack of treatment options available and the aggressiveness of the disease. The current standard of care for early-stage TNBC is neoadjuvant pembrolizumab in combination with chemotherapy followed by pembrolizumab monotherapy after surgery (KEYNOTE-522), however prior to this treatment options and outcomes have been relatively limited compared to hormone receptor- and HER2- positive breast cancers. This study aimed to describe the treatment patterns and clinical outcomes of early-stage and locally advanced TNBC patients in England before the approval of KEYNOTE-522. Methods: In this retrospective cohort study, data from the English National Cancer Registration and Analysis Service databases (Cancer Registry, Systemic Anti-Cancer Therapy, Hospital Episode Statistics [HES], National Radiotherapy Dataset and Diagnostic Imaging Dataset) were used. Adults with a first record of primary early-stage or locally advanced TNBC (stage II – IIIb) between 01/01/2015 and 31/12/2018 were indexed. Treatment pathways and clinical outcomes were investigated over a maximum of 5-years follow-up period extending to December 2020. Outcomes were described descriptively. Results: A total of 3,475 patients met the inclusion criteria for the newly diagnosed TNBC cohort. 82.7% and 17.3% of patients were diagnosed at stage II and stage III respectively and, 83.3% were of white ethnicity, and 46.6% were node positive. Around 80% of patients had a primary surgery performed (i.e. a mastectomy or breast conserving surgery). Anthracyclines were the most common drug type used as a first regimen in both the neoadjuvant and adjuvant settings. During the follow up period, 37.7% and 15.3% of patients experienced locoregional or distant metastatic progression, respectively and 22.6% died. Median OS or EFS was not reached as < 50% patients died within the 5-year follow up period. The 5-year OS and EFS rate was ~57% and ~60%, respectively. Increased healthcare resource utilisation (HCRU) with associated high costs was reported in the time periods post diagnosis. The mean number of TNBC-related inpatient stays was the highest in the 3 to 6 months following index; 3.77 (SD = 3.95), costing a total of £4,992,150.48 (per patient cost: £1,458.84 [£1918.76], mean [SD]). Conclusions: This is the first real world evidence study using the England NCRAS datasets to assess the outcomes of the early-stage and locally advanced TNBC population in England. Treatment plans were heterogenous in TNBC patients and probability of survival was poor. This highlights the need for improvement of the treatment options and thus clinical outcomes of this patient population.