Because these studies were analyzed only in the context of obese versus non-obese HER2-positive patients, including ER and/or PR positive and ER and PR negative breast cancer patients in the small sample size, these studies have not demonstrated whether an underweight BMI is associated with an increased risk of mortality relative to normal weight in the ER and PR-/HER2+ subgroup. This evidence concerns the gene ERBB2 and breast carcinoma.