Investigation of the protective and therapeutic effects of Lactobacillus casei and Saccharomyces cerevisiae in a breast cancer mouse model.

Introduction: The development of novel strategies for cancer therapy is crucial to improve standard treatment protocols.

Aim: This study aimed to determine the protective and therapeutic effects of heat-killed preparations of Lactobacillus casei and Saccharomyces cerevisiae in a breast cancer mouse model.

Methods: Forty-two female BALB/c mice (7-8 weeks old) were divided into six groups (seven mice per group). Four groups were injected with 10⁷ Ehrlich ascites tumor (EAT) cells suspended in phosphate-buffered saline (PBS) subcutaneously into the left side of the mammary fat pad. Tumor growth was monitored weekly until all animals developed a palpable tumor. The tumor-bearing mice in the experimental groups received heat-killed L. casei or S. cerevisiae three times per week for 35 days. The mice in the control group received PBS. The remaining two groups received heated L. casei or S. cerevisiae and then were injected with EAT cells. After 35 days, all mice were sacrificed to determine the immune response.

Results: Animals that received heated S. cerevisiae exhibited the lowest rate of tumor growth compared with the other groups. TGF-β and IL-4 secretion was increased in all mice, whereas the secretion of INF-γ and IL-10 was decreased in breast tissues. Moreover, at the histopathological level, the volume of viable tumor in the control group was higher than in the treated groups.

Conclusion: Supplementary treatment with S. cerevisiae resulted in the best outcome in the breast cancer model compared with other treated and vaccinated groups.