Human epidermal growth factor receptor 2 (HER2) subtype of breast cancer is aggressive, leading to a poor outcome. Targeted therapy with trastuzumab has been shown to be effective in the treatment of HER2-positive breast cancer. Cardiotoxicity is a specific adverse effect associated with trastuzumab. The initial formulation of trastuzumab was intravenous, but presently, a subcutaneous formulation (Herceptin SC) is available. Insufficient data on the response rate and cardiotoxic effects of trastuzumab among indigenous Black populations exist. In all studies evaluating the efficacy and toxicity of trastuzumab alone or in combination with chemotherapy, indigenous Black populations in Africa were not included, yet they are the ones most likely to benefit from highly effective cancer medicines. This is partly due to poor oncology clinical trial infrastructure in sub-Saharan Africa. The ARETTA study protocol (ClinicalTrials.gov identifier: NCT03879577) is a phase II multicenter feasibility study to evaluate the efficacy and toxicity of docetaxel given every 3 weeks for 4 cycles plus trastuzumab in 60 previously untreated women with nonmetastatic breast cancer. The primary endpoint is to assess the proportion of patients with complete pathologic response. Secondary endpoints include the number of patients who require dose delays in docetaxel and trastuzumab attributed to hematologic, GI, and cardiac toxicity. Pharmacokinetic profiles of subcutaneous trastuzumab will also be determined. The ARETTA study will provide important information on the clinical response and cardiac safety of subcutaneous trastuzumab in combination with docetaxel among indigenous African women with nonmetastatic breast cancer. It can also be used as a blueprint for conducting biomarker-driven oncology clinical trials in low-resource settings such as sub-Saharan Africa.