Link between breast cancer, obesity

Breast cancer is the leading cause of cancer deaths in women. More than 30 per cent of breast cancer patients are overweight or obese (body mass index of more than 24) indicating a clear association between body weight and breast cancer. Additionally, being overweight and obese are associated with poor breast cancer response to chemotherapy and immunotherapy. Body weight reduction is also linked to improved overall survival in overweight breast cancer patients.

Obese breast cancer patients also have high Ki-67 proliferative index. The Ki-67 is a protein released by proliferating cancer cells and a higher production rate of the protein is indicative of high rate of tumour growth.

A recent study shows that a high fat diet adjusts gut microbiota in favour of a bacterial species that produces amino acid called leucine. Leucine levels are higher in plasma of overweight/obese breast cancer patients than in breast cancer patients with lean body weight (body mass index of less than 24).

Leucine is transported in the bone marrow where it activates myeloid progenitor cells by triggering mammalian target of rapamycin receptor (mTOR) signalling pathway. This leucine induced activation of myeloid progenitor cells causes the cells to differentiate into polymorphonuclear myeloid suppressor cells (PMN-MDSC) which, on exiting the bone marrow, infiltrate breast tumour and suppress immune responses against the tumour, thus promoting breast cancer growth and poor prognosis. This is a clear indication of the existence of a gut-bone marrow tumour axis.

The gut bacteria that produce leucine in large quantities is known as Desulfovibro and its abundance in the gut is increased by a high fat diet. This finding is critical in use of precision nutrition targeting reduction of Desulfovibro in gut of overweight/obese breast patients in management and treatment of breast cancer.

Dr Mutua is the director, ImmunoBiologic Research and Consultancy Laboratory. [email protected]