According to the World Health Organization’s definition of overweight and obesity, adults with a body mass index (weight divided by height squared) ≥ 25 kg/m² are considered overweight and ≥ 30 kg/m² are obese. Metabolic syndrome is closely related to obesity and is a prognostic factor for obesity-related cancers in women, especially breast cancer. Metabolic syndrome refers to the pathological state in which the body’s protein, fat, carbohydrate and other substances undergo metabolic disorders, mainly including hypertension, dyslipidemia (high triglycerides, high LDL cholesterol, low HDL cholesterol), hyperglycemia (diabetes mellitus, high fasting glucose, glucose intolerance, insulin resistance, hyperinsulinemia), obesity (especially central obesity or called abdominal obesity, centripetal obesity), and fatty liver, which can cause a variety of cancers (including breast cancer, endometrial cancer, prostate cancer, pancreatic cancer, hepatobiliary cancer, and colon cancer). On March 14, 2018, the International Union Against Cancer’s International Journal of Cancer published online a study from Indiana University that showed that severity of metabolic syndrome, which is associated with an increased risk of death from all cancers and breast cancer, with waist circumference, blood pressure, and blood glucose being independent predictors of mortality risk for obesity-related cancers and breast cancer. Although being overweight is associated with many health risks, including heart disease and diabetes, it is not considered in current breast cancer screening guidelines. On March 15, 2018, the American Cancer Society’s Cancer published a study from the Karolin Institute in Sweden that found that for overweight women, there is a greater risk of undetected but rapidly enlarging breast tumors later in life, and frequent mammograms may be required. The results found that while both factors (body mass index and mammography density) were positively associated with tumor size at the time of breast cancer diagnosis, for interval cancers that occurred between routine mammograms every two years, only body mass index was associated with tumor size. In addition, for patients with spacer cancer, women with higher versus lower body mass index had a poorer prognosis, and mammography density did not correlate significantly with disease progression. Therefore, these results may help clinicians and patients to optimize screening decisions. Therefore, for overweight patients, breast cancer screening should be performed and a shorter screening interval should be considered. In addition, the risk of a poorer prognosis may be greater because the molecular tumor type and hormone receptor expression levels in overweight women make the cancer more difficult to treat.