Why is carcinoma of the breast more frequent in the upper outer quadrant? A case series based on needle core biopsy diagnoses.

The relatively high proportion of carcinomas arising in the upper outer quadrant of the breasts is argued to support the hypothesis that underarm cosmetics cause breast cancer. This study aimed to test the alternative hypothesis that the high proportion of carcinomas arising in the upper outer quadrant of the breasts is a reflection of the greater amount of breast tissue in this quadrant. The quadrant from which 746 consecutive breast core biopsies reported as normal, benign or malignant was recorded. The distribution in the breast of normal, benign and malignant results were comparable. In particular, the proportion of core biopsies from the upper outer quadrant reported as normal (67%, 95% confidence interval 59-74%), benign (57%, 95% confidence interval 51-63%) or malignant (62%, 95% confidence interval 57-67%) were similar. This result supports the hypothesis that the high proportion of upper outer quadrant carcinomas of the breasts is a reflection of the greater amount of breast tissue in this quadrant.