Bariatric Surgery May Eliminate Obesity-Related Breast Cancer Risk

Bariatric surgery for women with obesity was associated with a reduction in breast cancer risk that reached levels seen among those with a normal body mass index (BMI), researchers have found.

In their retrospective study of almost 70,000 women, an increased risk for incident breast cancer was observed in women who did not undergo bariatric surgery compared with women who did, after washout periods of 1, 2, and 5 years (P<0.001 for all):

• 1 year: HR 1.40 (95% CI 1.18-1.67)
• 2 years: HR 1.31 (95% CI 1.12-1.53)
• 5 years: HR 1.38 (95% CI 1.21-1.58)

The matched cohort study in JAMA Surgery from Mehran Anvari, MD, PhD, of St. Joseph's Healthcare in Hamilton, Ontario, and colleagues looked at five groups of women, divided evenly based on BMI category.

After a 1-year washout period, they found no difference in incident breast cancer in the bariatric surgery group compared with the cohort of women with a normal BMI (HR 1.07, 95% CI 0.89-1.28).

But the nonsurgical groups with higher BMIs had a significantly elevated risk for breast cancer at that point, ranging from 25-42%, compared with the bariatric surgery group, with similar results after 2- and 5-year washout periods as well.

Anvari and colleagues said the findings suggest "the carcinogenic associations between obesity and cancer risk are reversible and warrant public health attention given the current obesity crisis."

"The results of this study could have significant public health implications, given the increasing rates of both obesity and breast cancer," the researchers concluded. "Given the increasingly strong evidence supporting a reduced risk of breast cancer after weight loss, even among women at high risk of breast cancer, breast cancer risk reduction should be discussed as a benefit of weight loss."

In a commentary accompanying the study, Melissa L. Pilewskie, MD, and Justin B. Dimick, MD, MPH, both of the University of Michigan in Ann Arbor, wrote that while the findings are important, "the benefit of surgical weight loss may not be universal."

"In addition to lifestyle factors, several nonmodifiable risk factors, such as a genetic predisposition, strong family history, personal history of a high-risk breast lesion, or history of chest wall radiation, impart significant elevation in risk, and the data remain mixed on the impact of weight loss for individuals in these high-risk cohorts," wrote Pilewskie and Dimick.

Nevertheless, they observed, the evidence suggests a significant proportion of women could reduce their risk of breast cancer (and gain accompanying health benefits) after weight loss surgery.

This study included 69,260 women: 13,852 who underwent surgery for obesity (baseline BMI ≥35 with comorbid conditions or BMI ≥40) and 55,408 in the nonsurgical BMI cohorts. Mean age across the entire study population was 45.1 years, and the groups were balanced for age, cancer history, and breast cancer screening status. These women were followed for 5 years after bariatric surgery or index date (when BMI was measured).

In total, 659 breast cancers were diagnosed during the study period, in 0.95% of the study population. There were 103 breast cancers in the surgical cohort (0.74%). In the nonsurgical cohorts there were 128 in the BMI <25 group (0.92%), 143 in the BMI 25-29 group (1.03%), 150 in the BMI 30-34 group (1.08%), and 135 in the BMI ≥35 group (0.97%).

Across all cohorts, the most commonly diagnosed cancers were stage I. There were no significant differences across the groups for the distribution of stage, grade, or hormone status data.

The authors acknowledged several limitations to the study. Chief among these was the inability to adjust for healthy user bias since women in the surgical cohort may have been relatively healthier than the nonsurgical cohort in unmeasured ways, or made lifestyle changes that may have reduced their breast cancer risk.

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