Obesity may reduce the effectiveness of a common breast cancer treatment used on post-menopausal woman, a study has found.

A common breast cancer treatment for post-menopausal women may be less effective if the patient is obese, a new study has found.

Post-menopausal breast cancer sufferers are encouraged to take inhibiters which reduce the production of oestrogen, meaning there's less of the hormone to stimulate the growth of breast cancer cells.

But Auckland University's Professor Mark Elwood says the inhibitors may be less effective in obese women as they have more enzymes producing oestrogen in peripheral fatty tissue.

He's recently reviewed eight earlier studies to determine the effect of breast cancer treatment on obese patients.

The inhibitors are prescribed at a fixed dose for all patients, but co-author Dr David Porter says it's worth investigating if higher doses would be more effective in obese women.

And he said physicians should focus on more individualised treatment for patients who aren't responding to regular treatment.

More research was needed into whether different types of inhibitors might work better for obese patients, they said.

Earlier studies have also shown that obesity increases the risk of breast cancer.

Copyright AAP 2014