Hormone Receptor Testing (ER, PR)

Hormone receptor testing measures oestrogen receptor (ER) and progesterone receptor (PR) in tumour cell nuclei by immunohistochemistry. Tumours that express these receptors depend on hormone signalling for growth, and they respond to endocrine treatments that block the receptor or lower hormone levels.

The test is done on every new invasive breast cancer, and on recurrences and metastases when treatment depends on it. It is also used in endometrial, ovarian and some other cancers. It needs correct fixation, validated antibodies and controls.

Sections of formalin fixed, paraffin embedded tumour are stained, and the pathologist reports the percentage of positive tumour nuclei and the staining intensity. Results are ready in 1 to 3 days after the block is available.

About 70 to 80% of invasive breast cancers are ER-positive, and about 60 to 70% are PR-positive. ER-positive disease has a better outlook in the early years and a risk of late recurrence, and endocrine therapy for 5 to 10 years reduces recurrence and death substantially. The benefit is largest in tumours with strong, widespread expression.

Indications.

• All newly diagnosed invasive breast cancers, and ductal carcinoma in situ (for decisions on endocrine prevention).
• Recurrent or metastatic breast cancer, on a new biopsy when treatment depends on the receptor status.
• Male breast cancer.
• Endometrial cancer, and low grade serous ovarian cancer and endometrial stromal sarcoma, where endocrine treatment is used.
• Tumours of uncertain origin (breast and gynaecological origin in metastasis), and selected other tumours such as meningioma, where hormone dependence is considered.

Not indicated for non-hormone-dependent cancers, and not repeated on the same tumour without a reason.

Specimen requirements.

• Core biopsy or surgical specimen, fixed in 10% neutral buffered formalin as soon as possible (cold ischaemia time under 1 hour), for at least 6 hours and up to 72 hours.
• Sections cut fresh and stained with a validated antibody and platform, with positive and negative controls in each run.
• Decalcified bone metastases need EDTA, and the result is interpreted with caution.
• Cytology cell blocks, with the same fixation rules.
• Clinical details: tumour type, side, and previous receptor status.

Normal appearances.

Normal breast ducts serve as an internal control and show variable nuclear staining in a minority of luminal cells. A valid test has staining in normal ducts, and positive and negative control tissues behave as expected.

Interpretation.

• Positive: 1% or more of invasive tumour nuclei stain, and the percentage and intensity (weak, moderate, strong) are reported. Scores such as the Allred score (0 to 8) or the H-score (0 to 300) summarise this.
• ER-low-positive: 1 to 10% of cells stain. The benefit from endocrine therapy is less certain, and these tumours often behave like triple negative disease. The report notes the finding and the uncertainty.
• Negative: under 1% of nuclei stain, with valid internal controls. Tumours that are ER, PR and HER2 negative are triple negative.
• PR: positive at 1% or more. PR adds prognostic information, and ER-positive with PR-negative disease may respond less well to endocrine therapy.
• Discordance between a primary tumour and a metastasis occurs in 10 to 20%. Loss of ER at relapse changes treatment, so the most recent tumour is tested.
• Endocrine therapy choice: tamoxifen, aromatase inhibitors, ovarian suppression and other agents, selected by menopausal status and risk.
• Receptor status is combined with grade, HER2, Ki-67 and, where used, genomic risk scores to decide on chemotherapy.

Critical values and findings needing immediate action.

• An ER-positive result in a patient with metastatic breast cancer: endocrine therapy, with or without targeted agents, is started by the oncology team.
• A triple negative result: referral for chemotherapy and testing of other markers (PD-L1, BRCA1 and BRCA2).
• An invalid or equivocal result (poor internal control): repeat on another block or a new biopsy.
• Unexpected ER positivity in a tumour of uncertain origin: communication to the oncology team.

Limitations and artefacts.

• Under fixation (fixation under 6 hours), delay to fixation, hot or cold ischaemia and acid decalcification lead to false negative results, and are the main cause of discordant results between laboratories.
• Over fixation causes weaker staining, and old sections lose antigenicity.
• Edge artefact, necrosis and crushed areas are not scored, and in situ carcinoma must be separated from invasive carcinoma.
• Heterogeneous expression: a small biopsy may not represent the whole tumour.
• Subjective scoring, particularly at the 1% and 10% boundaries, and variation between observers, so quality assurance and external review matter.
• A negative result with no internal control staining is not valid.
• Receptor results can change with treatment (endocrine therapy, chemotherapy), and after neoadjuvant treatment the post-treatment tumour is retested.
• Immunohistochemistry does not detect functional resistance, such as ESR1 mutations, which develop under treatment.

Special groups.

• Premenopausal women: ovarian suppression is added in higher risk disease.
• Men with breast cancer: the same testing, and most tumours are ER-positive.
• Older women: endocrine therapy alone may be enough in low risk ER-positive disease.
• Patients with metastatic disease: re-biopsy for receptor status, and a plasma test for ESR1 mutations at progression.
• Pregnant patients: treatment is planned with specialist input.
• Regions: hormone receptor testing is the most useful and cost effective molecular test in breast cancer, because tamoxifen and aromatase inhibitors are cheap, effective and widely available. Fixation quality and delays in transport are the main problems. Where testing is not available, endocrine therapy is sometimes given on clinical grounds to postmenopausal women, and tumour features, grade and node status are used to decide.

Follow up tests.

• HER2 testing (immunohistochemistry and in situ hybridisation).
• Ki-67 proliferation index and tumour grade.
• Genomic risk tests (multigene assays) in selected ER-positive, HER2-negative disease.
• BRCA1 and BRCA2 and other germline testing for eligible patients.
• Bone density and gynaecological assessment during endocrine therapy.
• Repeat receptor testing on a metastatic biopsy.
• Staging imaging for higher risk disease.
• Multidisciplinary meeting.