Protective effects of a probiotic yoghurt in a murine model of breast cancer undergoing chemotherapy

Breast cancer is one of the most frequently diagnosed cancers worldwide. Although chemotherapy remains a prevalent treatment, it negatively affects patients’ quality of life. In this regard, probiotics emerge as possible adjuvants. The aim of this study was to evaluate two lactic acid bacteria (LAB) selected for their immunomodulatory properties, <i>Streptococcus thermophilus</i> CRL807 and <i>Lactobacillus delbrueckii</i> subsp. <i>bulgaricus</i> CRL864, in a breast cancer model undergoing chemotherapy with capecitabine or 5-fluorouracil (5-FU). 4T1 breast cancer cells were injected into the upper mammary gland of adult female mice. After tumour reached an appropriate size, mice were separated into groups (<i>n</i> 10) receiving either individual LAB (100 µl of 9 ± 1 × 10⁸ CFU/ml) or yoghurt (2 ± 1108 CFU/ml <i>ad libitum</i>) with or without chemotherapy. The results showed that administration of LAB or yoghurt resulted in a significant reduction in tumour size and weight (about 50%), modulating the immune response, with increases of IL-10 in mice with smaller tumours, and without affecting chemotherapy. Furthermore, consumption of LAB or yoghurt decreased the negative side effects associated with these treatments. Yoghurt showed the best results in preventing weight loss, with lower mortality (20 % <i>v.</i> 40 % for 5-FU treatment), maintaining intestinal histology and modulating plasma cytokines, with increases of IL-10. In conclusion, administration of this probiotic yoghurt was safe in cancer hosts undergoing chemotherapy, reducing some associated negative side effects without interfering with the primary cancer treatment. Furthermore, this yoghurt showed beneficial properties against the tumour, modulating the host’s immune response.