There is increasing knowledge of the relationship between obesity and breast cancer, obesity and breast cancer recurrence, and reconstructive outcomes in obese patients.
There is an association between post-menopausal breast cancers and obesity. This relationship is significant given the recent statistics showing 40% of patients over age 60 are obese. There are studies that suggest that obese, post-menopausal breast cancer patients are at higher risk of estrogen-positive breast cancers, as well as triple-negative breast cancers. http://www.livescience.com/13030-obesity-increase-risk-aggressive-breast-cancer.html
With regards to breast cancer recurrence, the relationship with obesity is quite ominous. When looking at hormone receptor positive breast cancers (the most common type), and after excluding patients with other medical problems, researchers found higher BMI alone predicts a higher rate of recurrence and premature death. This finding is despite meeting adequate standards of care with surgery, chemotherapy, and hormonal therapy. This link summarizes the findings of the study.
With regards to breast reconstruction, recent outcome studies have shed light on additional risk of complications in the obese. Obesity is a significant risk factor for failure with implant-based reconstruction done at the same time as mastectomy (immediate reconstruction); this issue is more pronounced in the morbidly obese (BMI > 35) and tends to correlate with breast size. In a study out of MD Anderson in 2012, failure rates of immediate implant reconstruction in the obese population (BMI 30-35) was 11%, and in the morbidly obese population (BMI >35) it was 25%. Contrast this to abdominal free flap reconstruction (DIEP flap or muscle-sparing TRAM flap), which showed failure rate of roughly 1% across all patient populations. Based on this data, as well as our ability to achieve good aesthetic outcomes in the obese, DIEP flap reconstruction is most advantageous in the obese.