Bigger is not better! The risk of obesity and risk of breast cancer incidence and recurrence in the Indian subcontinent.

Review of data from the national cancer registry program of ICMR[1] suggests that 1 in 28 women in urban India and 1 in 64 women in rural India are at risk of developing breast cancer. This is in sharp contrast to the data from the west[2] wherein 1 in 8 women are at risk of developing breast cancer. The disparity in risk of urban and rural India may be explained by many factors including the difference in lifestyle, where women in urban India are adopting the changes from the west. Breast cancer care has evolved over the years towards more sophisticated targeted therapy and personalized care. For a disease so well researched, we are still to understand the complexities of the impact of lifestyle changes and their role in risk of disease incidence and recurrence.

Obesity is a modifiable risk factor that has been highlighted in breast cancer research in the recent years. Multiple studies[3] have evaluated the role of weight gain as a risk factor for the development of post-menopausal breast cancer and its negative impact on prognosis. The probable mechanisms by which obesity affects cancer cells are hormonal changes,[4] such as elevated serum estrogen levels, local production of estrogen and inflammation.[5] Another theory is that overweight and obese women may be more insulin-resistant and, therefore, have more insulin, which is postulated to trigger the growth of breast cancer cells.[6]

Research has found that the association between excess weight and cancer recurrence and death is strongest among women with estrogen receptor-positive breast cancer. The EPIC study[7] suggested that 7%-15% of breast cancer is caused by obesity and that obese women have a 30% higher risk of post-menopausal breast cancer than women in the regular weight group. A study from India also revealed a strong association of overweight and obesity with breast cancer in the Indian population.[8]

Obesity has been consistently associated with an increased risk of post-menopausal breast cancer. Recent data also suggests an association of obesity with pre-menopausal breast cancer risk. Data from two large chemoprevention trials,[9] showed that there was a 70% increased risk of breast cancer in obese pre-menopausal women (vs. normal weight).

The authors Singh et al.[10] have evaluated the risk of breast cancer and BMI in women presenting to a university hospital in northern India. Their study suggests an increased risk of developing breast cancer as the amount of visible fat intake increased. The risk of developing cancer was almost half (OR low fat vs. medium fat is 0.497, 95% CI 0.267-0.925) in subjects who had taken low amount of visible fat, and about five times in those with high fat intake (OR high fat vs. medium fat is 5.255, 95% CI 2.584-10.688, P < 0.0001).

The relation between BMI and visible fat intake was also found to be statistically significant in pre-menopausal and post-menopausal women. Additionally 42.2% presented in the fourth stage of cancer, suggesting a lack of awareness regarding breast cancer among the study population.

The authors have aptly highlighted that mere lifestyle changes and weight reduction would reduce the incidence and risk of recurrence in breast cancer. This, however, needs more research into the possible mechanisms and role of IGFR and insulin resistance in obese and overweight individuals. The next step may be to evaluate the role of tailoring therapy in breast cancer patients with specific interest in overweight individuals to duration of treatments and IGFR manipulation.