A new study presented this week at the American Association for Cancer Research (AACR) Breast Cancer Symposium in San Antonio has found that obesity is associated with poor prognosis in women with early-stage breast cancer, confirming the results of previous studies. To conduct the study, the authors examined data concerning 4,368 breast cancer patients treated at Baylor College of Medicine during the period 1970 to 1995. For the study group as a whole, women who were overweight at diagnosis were found to have similar outcomes as normal weight women. However, obese women were more likely to experience shorter time to recurrence, worse relapse-free survival rates, and worse overall survival rates. When only the women who did not receive chemotherapy or anti-estrogen (aromatase inhibitor or tamoxifen) treatment were considered, a trend for worse survival outcomes (which did not reach statistical significance) was found for obese patients compared to normal weight patients. However, when only women who received chemotherapy were analyzed, obese women were found to have substantially worse outcomes than normal weight women. In other words, obesity might interfere with the effectiveness of chemotherapy or the ability to determine and administer appropriate dosages.

On the other hand, overweight women who received endocrine therapy, mainly tamoxifen, had significantly better outcomes than normal weight women. In other words, obesity appeared to confer a protective effect in women taking tamoxifen. "Obesity is a probable risk factor for worse breast cancer outcomes, and ours is the latest study to suggest it has an effect on treatment outcome as well,” said lead researcher Sao Jiralerspong, an assistant professor of medicine at Baylor. Jiralerspong also said that the “finding that overweight patients have a better outcome than normal-weight patients after tamoxifen treatment is surprising. " More research is needed to understand the effect of body weight on adjuvant breast cancer treatment, according to the authors, because of the unexpected findings and because additional drugs are in use today compared with the time period studied.

Other San Antonio conference results concerning obesity

Several other studies concerning obesity and breast cancer were also presented at the conference (see the first three studies listed below):

• Increases in the intake of starch (such as that found in white bread, white potatoes, and corn starch) during the first year after diagnosis are associated with reduced survival in women with lower-grade tumors.
• Having type 2 diabetes or being obese after 60 years of age significantly increases the risk of breast cancer among Swedish women. Obesity in women after age 60 increased the risk for developing breast cancer by 55%. The study also reported that insulin glargine (Lantus) use almost doubled the risk of developing any cancer, including breast cancer, adding to the unfavorable data concerning this type of insulin and breast cancer.
• An intermittent, low-carbohydrate diet is superior to a standard calorie-restricted Mediterranean diet for seven days per week for reducing weight and lowering circulating insulin levels.

What should obese breast cancer patients do?

Obese women know that they should lose weight and a diagnosis of breast cancer can reinforce this message. Given that it is impossible for anyone to move quickly from being obese to being merely overweight, what can such women do to improve their prognosis? First, it should be noted that to date no study has confirmed that losing a substantial amount of weight after a diagnosis of breast cancer improves survival (such studies simply do not exist). Second, it might be quite beneficial to address factors associated with obesity that contribute to breast cancer progression, namely, increased inflammation, higher blood glucose, insulin and estrogen levels, and leptin and other growth factors produced by fat cells. Based on available evidence, below are some practical steps that obese women take to reduce their heightened risk of recurrence:

• Avoid gaining weight during breast cancer treatment. While the public perception may be that cancer patients lose weight, this is only true of end-stage disease. A large minority of women gain weight during chemotherapy and anti-estrogen treatments can also promote weight gain.
• Undertake regular exercise. Only light to moderate exercise is advisable during chemotherapy or radiation treatment. However, after this, a consistent and sustained daily program is advisable. For very obese women, this might mean walking only one block at first (a meaningful amount of exercise for them). This will reduce inflammation and improve glucose metabolism, among other benefits, even if it is not accompanied by weight loss.
• Adopt an anti-inflammatory diet. The foods recommended in this website are for the most part anti-inflammatory and have the added benefit of being associated with reduced breast cancer risk. Please see our article on how to optimize your breast cancer diet. Following such a diet will also result in weight loss without counting calories or greatly restricting overall intake, however it is by no means easy to make the transition to this way of eating.
• Avoid blood sugar and insulin spikes. Try to keep meals under 500 calories and make fiber and protein a part of each one.
• Get enough sleep. For most women, this means at least seven hours per day.
• If you have hormone receptor positive breast cancer and are going to receive endocrine treatment, discuss the obesity issue with your oncologist. There is some evidence that obesity interferes with aromatase inhibitor treatment whereas it does not appear to do so for tamoxifen. Therefore, it is possible that tamoxifen may be preferable for many obese women despite evidence that aromatase inhibitors are generally more effective. Please see our article on the impact of endocrine therapy on breast cancer prognosis.