To improve the accuracy of ER and PR testing, ASCO and the CAP recommend the following:

• The ER and PR status should be tested on the primary tumor and/or areas of spread (called metastases) for each patient newly diagnosed with invasive breast cancer or a breast cancer recurrence.
• A tumor is ER and/or PR positive if at least 1% of the cells examined have estrogen and/or progesterone receptors, and for such a tumor, patients should talk with their doctors about considering hormone therapy.
• Testing is best done on larger tissue samples. If the cancer has spread, testing on those areas may be considered as well.
• Laboratories testing for ER and PR should be accredited by the CAP or meet the additional accreditation requirements in the guideline and show agreement with other validated ER and PR tests for both positive and negative results. The laboratory must also be inspected every two years to be sure that the testing methods conform to the guideline requirements.