Tom is a 12-year-old boy who presents with a 6-month history of breast enlargement. He is extremely embarrassed about the size of his breasts and avoids sport because he does not want to be seen while getting changed. He wonders if anything can be done to reduce the size of his breasts.

Tom has Tanner stage III breast development. He has entered puberty and his height and weight are both on the 99th centile. He has a male karyotype and his hormone levels are all within the normal range.

As Tom is so distressed, you decide that something needs to be done. You have heard that anti-oestrogens, such as tamoxifen, and aromatase inhibitors, such as anastrozole, can be used to treat pubertal gynaecomastia. You start Tom on 10 mg of tamoxifen daily, but after 6 months of treatment this has made little difference to the size of his breasts. You wonder whether anastrozole would be a more effective therapy.