In this experimental study, a protocol was developed for processing a formulation derived from secretome obtained from adipose tissue mesenchymal stem cells at different concentrations. Its molecular composition and in vitro efficacy was evaluated when applied to breast cancer cell lines. In addition, the ability of the formulation to suppress the growth of triple-negative breast cancer when infused into a mouse model of the disease was verified. The efficacy of the formulation both as monotherapy and as adjunctive therapy in combination with paclitaxel was also evaluated. In vitro, significant tumour cell killing was observed at a formulation concentration of 20mg/ml, which was not toxic to non-tumour cells. In vivo, no tumour growth was detected following a daily intra-tumour infusion of the formulation at doses of 50mg/ml and 100mg/ml. This study, therefore, suggests that a formulation obtained by secreting stem cells from adipose tissue represents a potential biotherapeutic agent for the treatment of breast cancer and can be used initially as an adjunct therapy to other standard therapies in a way that improves efficacy without generating adverse events.