What are the roles of BRCA1/BRCA2 and HER2 status in breast cancer care?

Screening

Breast cancer is the most common cancer in women, affecting about one in eight in the UK.

Systematic breast cancer screening strategy

Whom is it for? 

Women between 50 and 71 years of age are screened, usually every three years, even if they have no symptoms or risk factors. It is considered that from 50 to 71 years of age (post-menopause), a woman has a higher risk of developing breast cancer.

Women with risk factors (such as a family history of breast cancer) are prioritised with personalised surveillance. Indeed, with this cancer it is important to take family health history into account. Recommendations for screening vary according to the patient's history: monitoring takes place more frequently and earlier in "at-risk" women.

What are the screening tests?

Every three years, screening consists of a mammogram and a clinical examination (palpation and a patient interview). Further exams can then complete the diagnosis: biopsy, MRI or even an ultrasound.

The aim of this screening is to detect any non-palpable breast lesions or any form of asymptomatic cancer. Indeed, when detected early, breast cancer has a 90% chance of being cured.

Genetic testing: BRCA1 and BRCA2 gene mutations

Why undergo genetic testing?

The occurrence of breast cancer is thus often linked to a woman's family history and the presence of specific mutations. Detecting mutations through genetic testing is a key part of diagnostic strategy and plays an important preventive role.

Not only hereditary mutations!

It should be noted that the development of this type of cancer facilitated by the underlying existence of hereditary mutations in the BRCA1 and BRCA2 genes, and more rarely in the PALB2 gene. These 3 genes are most implicated (2 to 5%) in the development of breast cancer, but other predisposition genes have recently been identified.

The risk of developing breast cancer in the general population is 12%. However, this risk increases significantly in the population presenting genetic mutations:

• With BRCA1: the risk reaches 45% before the age of 50 and 70% before the age of 80;
• With BRCA2: the risk reaches 35% before the age of 50 and 70% before the age of 80.

The notion of risk refers to the idea that one can be a carrier of one of these mutations and develop the cancer, but also leaves the possibility that, by being a carrier, the cancer will never develop.

When a family predisposition for cancer is discovered, it is recommended to offer genetic testing to relatives to help identify which family members are predisposed and recommend appropriate follow-up, or to reassure those who do not carry the mutation.

All that being said, the presence of genetic mutations is not always related to family history. In 50% of women with one of these mutations, there was no family history of cancer. This is why it is very important to study the individual risks: smoking, alcohol, diet, and lifestyle. Health authorities have even raised the question in recent years of whether to broaden the recommendations of genetic testing for cancer.

Following the detection of the BRCA1 and BRCA2 gene mutations, patient care can range from simple close monitoring to preventive surgery (mastectomy, removal of the mammary gland, in anticipation).

HER2 status

Beyond the important preventive aspect, genetic testing also plays a predictive role. When a cancer is confirmed, its genetic characterisation can be used to predict the evolution of the disease, its prognosis (aggressiveness and metastases) or the efficacy or resistance of a treatment. For example, certain targeted therapies are better suited or more effective in treating cancers caused by a specific mutation. Knowing the genetic signature of the cancer guides therapeutic choice, the aim being to personalise the treatment as much as possible. 

The HER2 status is systematically looked for in women who have been diagnosed with breast cancer. The biopsy sample is used to look for the genetic anomaly.

What is HER2?

HER2, short for "human epidermal growth factor receptor 2", is a protein naturally present in breast cells that is involved in normal cell proliferation and growth. HER2, when produced in larger than normal amounts, can lead to the formation of tumours. Indeed, when it is on the surface of breast cells, it stimulates their growth.

How is it detected?

Today, two examinations can be carried out:

• Immunohistochemistry (IHC): this is the most common test for HER2 and is performed on biopsied breast tissue. The test quantifies the presence of HER2 protein on the surface of the cancer cells and gives a score of 0 to 3+. A score of 0 to 1+ means it is HER2-negative, a score of 2+ is "borderline", and a score of 3+ is HER2-positive.

or

• Fluorescence In Situ Hybridization (FISH): this test is also done on biopsied breast tissue and is used to visualise the genetic material in the patient's cells. The test examines how many copies of the HER2 gene there are in the cell, so the more copies of the HER2 gene there are, the more HER2 receptors the cells have. The results will indicate if the cancer is positive or negative for HER2.

Depending on the amount of HER2, the tumour is said to be HER2-positive or HER2-negative. 12 to 20% of breast cancers are HER2-positive. In these cases, targeted anti-HER2 therapy may be offered.

Targeted anti-HER2 therapies

Targeted drug therapies have become the first choice for the treatment of HER2-positive breast cancer. These therapies precisely and specifically target the mechanism of development and survival of tumour cells. Unlike more conventional chemotherapies where the mode of action is aimed at destroying cancer cells, the aim here is to starve the tumour and deprive it of growth factors. 

Targeted anti-HER2 therapies are administered intravenously or subcutaneously. These include trastuzumab (Herceptin®), pertuzumab (Perjeta® and Kadcyla®) or lapatinib (Tyverb®).

This method of treatment has really improved patient care and the prognosis for breast cancer.

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