Association of Bariatric Surgery Status with Reduced HER2+ Breast Cancers: a Retrospective Cohort Study

Bariatric surgery is associated with a reduced risk of developing certain malignancies, particularly in women. However, the impact of bariatric surgery on tumor characteristics, cancer treatment, and oncologic outcomes is unknown.

In a retrospective cohort study, 42 subjects diagnosed with breast cancer after bariatric surgery (1989-2014) were matched to 84 subjects with breast cancer (1984-2012) who did not undergo bariatric surgery, based on age, body mass index (BMI), and menopausal status at the time of breast cancer diagnosis, as well as the date of cancer diagnosis. Medical records were reviewed for cancer and bariatric endpoints. Statistical analysis was performed using mixed effects regression models, generalized estimating equation, conditional logistic regression, and Fisher's exact tests.

Women who developed breast cancer after bariatric surgery presented at an earlier stage compared to non-operated, obese controls. In the bariatric surgery group, there were fewer tumors with human epidermal growth factor receptor 2 overexpression (HER2+) (OR 0.16 (0.03-0.76); p = 0.02), with no significant differences seen in estrogen and progesterone receptor positivity. No HER2+ cancers were found in patients who underwent Roux-en-Y gastric bypass (OR 0.00 (0.00-0.43); p = 0.002). On multivariate analysis, bariatric surgery status remained associated with reduced HER2+ breast cancers (OR 0.18 (0.03-0.99); p < 0.05). At a mean follow-up of 5 years, bariatric surgery was associated with trends toward reduced cancer-specific and all-cause mortality.

Bariatric surgery is associated with reduced HER2+ breast cancers, suggesting that bariatric surgery can influence breast cancer characteristics and, potentially, tumor biology.