Recently, an international research team, with the participation of the University of Granada, Spain, revealed why the incidence of breast cancer is higher in the obese population, the reason being that the paracancerous fat (fat surrounding the tumor) promotes the expansion and invasion of tumor stem cells, which are responsible for the development of the tumor, and the related results were published in Cancer Research. Tumor stem cells make up a small percentage of the tumor and are mainly characterized as being responsible for metastasis away from the primary tumor and cannot be eliminated by conventional chemotherapy and radiotherapy, and are usually effective at the beginning of treatment, but many patients face recurrence. Mechanisms have not been elucidated The impact of obesity on cancer morbidity and mortality is severe, and it is estimated that up to 20% of cancer deaths are related to obesity. Obese women are at greater risk of developing breast cancer after menopause, and the progression of disease is worse in obese women and is independent of age. The mechanisms by which obesity affects cancer development are not yet clear, and the fat associated with obesity is known to cause local inflammation and prevent the maturation of lipid cells. In the current study, researchers used mice to assess the effects of adipocytes co-cultured with breast cancer cells on tumor aggressiveness and metastatic capacity. The results showed that interactions between tumor cells and immature adipocytes surrounding the tumor promote the secretion of cytokines (pro-inflammatory proteins) during the first stages of breast cancer development. Juan Antonio Marchal Corrales, professor at the University of Granada, co-author of the paper, explained, “These cytokines cause a high degree of metastasis of tumor stem cells.” Clinical rationale In addition, the researchers describe the mechanism by which the process occurs and the effect on it of the activation of SRC protein kinase, a protein that induces the activation of the Sox2 transcription factor (which maintains tumor stem cell properties) and the small molecule RNA, miRNA-302b. Tumor cells co-cultured with immature adipocytes increased the proportion of tumor stem cells and tumor cells in the blood and increased the metastatic capacity of tumors in mice,” said Prof. Marchal. Finally we found that SRK kinase inhibitor drugs reduced the production of cytokines and tumor stem cells.” This study provides new insights into the mechanisms by which obesity increases breast cancer mortality and gives new clinical rationale for testing the clinical efficacy of SRC inhibitors.