Breast Cancer Tumour Receptors

Receptor Status plays an important role in the treatment of Breast Cancer.

Hormone Receptor Status is required to start the patient on endocrine therapy.

What is Endocrine therapy?

Endocrine therapy is the type of treatment that deals with hormones and their action. It involves the addition, blockade or removal of hormones. In the case of breast cancer endocrine therapy mainly deals with the blockade or reduction of estrogen levels, a hormone which is implicated in the development of breast cancer.

Endocrine therapy against estrogen in breast cancer decrease the rate of tumor cell proliferation and lead to death of tumor cells.

Trastuzumab which is a monoclonal antibody is started once HER2 receptor status is confirmed. Monoclonal antibodies are antibodies from the same parent cell.

Once a patient is diagnosed with breast cancer, the tissue samples obtained from core biopsy are sent for immunohistochemistry to determine estrogen, progesterone and HER2 receptor status. If the tumour has a significant amount of ER/PR receptors they are considered as hormone receptor positive. Estrogen receptors respond to estrogen whereas progesterone receptors respond to progesterone.

The receptor status determines the course of treatment- Whether the patient will benefit from hormonal therapy or chemotherapy.

The receptors present in breast cancer cells act like a type of switch which may be either ‘on’ or ‘off’. When these switches are acted upon by chemotherapy or targeted therapy, they are in the ‘off’ position causing the tumour cells to stop division and to eventually die.

Breast cancer tumour receptors

Estrogen receptors

The cells which have these type of receptors respond and grow to estrogen. Treatment with anti estrogen hormone(endocrine) therapy can block the growth of these tumour cells.

These receptors are located within the cytosol of the cell. Estrogen diffuses across the cell membrane and then binds to these receptors and produces a conformational change in them and then translocates into the nucleus.

Estrogen is a steroid hormone synthesised from cholesterol. A number of tissues such as breast tissue, liver contains enzymes that synthesize estrogen.

Image result for aromatase enzyme

Ultimately estrogen is made from testosterone which was its final precursor, by the action of the enzyme aromatase. Breast adipose cells and cancer cells synthesize their own estrogen and these levels can be higher than that in plasma.

Image result for estrogen receptors staining
Nuclear staining seen in estrogen receptor positivity, cytoplasmic staining is considered negative

There are two types of estrogen receptors-

ER alpha– classic ER receptor, expressed in breast and epithelium. These receptors are responsible for proliferation.

ER beta– These have housekeeping functions. They are found in granulosa cells of ovary.
Housekeeping genes are genes responsible for basic cellular function.

Progesterone receptors

Proteins which bind to progesterone. These belong to the superfamily of steroid receptors just like estrogen receptors. These receptors, just like estrogen receptors translocate into the nucleus from the cytosol after binding to progesterone.

The role of progesterone receptors in endocrine therapy is not clear. Progesterone receptors are said to modulate estrogen receptors. Progesterone stimulation of breast cancer cells, can modulate estrogen receptors leading to changes in gene expression profile, leading to cell cycle arrest.

In simpler words progesterone receptors have a negative effect on estrogen receptors decreasing their activity. Preclinical studies have shown that addition of progesterone may benefit patients with breast cancer.

In vitro growth of tumour cells were seen to have been inhibited by progesterone receptor modulators especially in estrogen receptor positive tumours.

Risk Factors in developing estrogen positive breast cancer

Sex– Females are more likely than males to have breast cancer, but in males 90% breast cancers are estrogen positive as compared to females in whom 80% of breast cancers are estrogen positive.

Age– Hormone receptor positive breast cancer becomes more likely in older age groups.

Lifetime exposure– Those females who attained early menarche and late menopause or those who are on hormone replacement therapy to relieve menopausal symptoms are at a greater risk of developing hormone receptor positive breast cancer.

Breast feeding– Breast feeding reduces estrogen exposure thus reducing the chances of hormone positive breast cancer.

Lifestyle– High Body mass index(BMI) and lack of physical activity, excess alcohol consumption. These factors increasing the chances of hormone positive breast cancer.

Tests for hormone receptor status

Test for estrogen status are done using special staining techniques, called Immunohistochemistry. Not all labs use the same method and hence the results may vary. The pathology report may have the following:

Immunohistochemistry is a tehnique by which specific antibodies are used which bind to specific proteins thereby confirming a particular type of tumour.

A percentage that that tells how many cells out of 100 stain positive for the hormone receptor, this may vary from 0 to 100%.

An Allred score ranging from 0-8- this scoring is based on the percentage of cells that stain positive for estrogen receptors and how well they show on the film after staining, this is called ‘intensity’.

Image result for allred scoring
Allred scoring is done by adding Proportion score and Intensity score. Score of 0-2 is considered negative and 3-8 is considered as positive.

Different labs have different cutoffs. A score of zero generally means that the tumour is hormone receptor negative and that the tumour will not be responsible for hormone therapy. A score of 1- 10 % cells showing positivity for hormone receptors may be considered positive in some labs and negative in another. Studies have shown that even low number of hormone receptors can respond to endocrine therapy.

Interpreting test results

ER positive– Seen in 80% of the breast cancers. It means that the tumour is estrogen receptor positive.

ER+/PR+– Seen in 65% of the breast cancers that are estrogen positive. This means that both the receptors are present.

ER+/PR- – Seen in 13% of breast cancers

ER-/PR+ – Seen in 2% breast cancer cases. It means that progesterone may be supporting the growth of this cancer. The role of progesterone receptors in breast cancer is still being studied.

ER-/PR– These tumours stain negative for hormone receptors. These tumours have a poor prognosis.

In case any one of either estrogen and progesterone are positive or both are positive, the breast cancer is considered ‘hormone positive’.

If the samples are positive for hormone receptor status, endocrine therapy will form a part of the treatment.

HER2 Receptors

These are transmembrane receptors that drive some of the most aggressive breast cancers. They belong to receptor Tyrosine kinase family. These receptors are responsible for receptor mediated intracellular signalling resulting in cells to proliferate aggressively.

Image result for HER2 receptor staining
HER2 receptor positivity will show cytoplasmic staining

To detect HER2 FISH(Fluorescent in situ hybridisation) is used. In this technique a fluorescent probe is used which binds to HER2 locus on chromosome 17 and the centromere of chromosome 17.

Image result for fish technique
In FISH technique a specific probe is used that binds to a particular gene producing a fluoresence

CISH(Chromogenic ISH) and SISH( Silver enhanced ISH) can also be used to detect HER2 status, using peroxidase enzyme.

Interpretation of results

—>An IHC staining of 3+( uniform and intense staining of greater than 30 % of invasive tumour cells) or FISH result of more than 6 HER2 gene copies per nucleus or a FISH ratio of greater than 2.2 is considered positive for HER2 receptor.

—>An IHC staining of 0-1+ , or FISH result of less than 4 HER2 gene copies per nucleus, or a FISH ratio of less than 1.8 is considered negative for HER2 receptor.

What is FISH ratio? It is the ratio of HER2 gene signals to chromosome 17 signals. Cancers that have more than one chromosome 17 are more likely to have more copies of the HER2 gene. The HER2

Around 20% of breast cancers have overexpression of the HER2 gene. These tumours are treated with Trastuzumab, which block the HER 2 receptors, leading to clinical benefit.

Types of breast cancer based on hormone receptor status and HER2 status

Luminal type A( ER+/PR+/HER2-ve)– These tumours are responsive to hormone therapy and have a good prognosis. 15% of tumours which have a p53 gene mutation have a poor prognosis.

Luminal type B-(triple positive breast cancer)– These cancer can be treated with both hormonal therapy as well as drugs that target HER2 receptors.

ER-/PR- and HER2 +ve breast cancer-These tumours are diagnosed at a younger age as compared to hormone positive breast cancer. They are highly aggressive tumours treated with trastuzumab.

Basal-like(triple negative breast cancer)– these tumours have hormonal and HER2 receptor negative status. They are called basal like because of the tumour cells that have features similar to those of the basal cells that surround the mammary ducts. It should be noted that all triple negative breast cancers do not resemble basal cells and vice versa.

The triple negative breast cancers can be further divided into two subgroups based of EGFR(epidermal growth factor receptor) and cytokeratin 5/6. These subgroups are core basal and 5-negative phenotype(5-NP).

The core basal is positive for EGFR and cytokeratin 5/6 whereas the 5-NP is negative for EGFR and cytokeratin 5/6. The core basal has a worst prognosis as compared to 5-NP.

ASCO HER2 testing guidelines

—>HER2 must always be tested on newly diagnosed breast cancer cases.

—>Atleast one tumour sample must be tested for HER2.

—>Discuss the role of HER2 targeted therapy if the HER2 test is positive, and delay to recommend targeted therapy if the test is equivocal.

—>Mandatory testing must be done on the same specimen if the initial HER2 result is equivocal using an alternative test, or on an alternative specimen.

—>Do not administer targeted therapy if the HER2 result is negative.

—>If technical issues prevent IHC or ISH tests from being done in a specimen report the test as indeterminate.

—>In rare cases it may be difficult to know if the HER2 status is positive or negative. In these cases all the clinical data on the patient should be considered before starting chemotherapy.

HER2 positivity indicate more aggressive tumors with a higher risk of recurrence after treatment. Drugs such as trastuzumab have been developed that act against HER2 receptors, but despite these successes patients often dont benefit from this treatment and often show resistance after initial treatment.

Breast cancer treatment depends on many aspects such as staging, genomics etc. The receptor status forms a crucial part of these aspects. It is mandatory that breast cancer receptor status must be done as early as possible so that the doctor as well as the patient can make the right treatment decision.

Leave a Reply