Human epidermal growth factor receptor 2 (HER2) is a gene that can play an important role in the development of some types of breast cancer. This gene is also sometimes referred to as Erc-B2 receptor tyrosine kinase 2 (ERBB2). This gene is involved in the production of HER2 proteins, which are present on breast cells as receptors to control the growth, division, and repair of the cells.

Testing and pathology report

When a woman is diagnosed with breast cancer, she will receive a pathology report that indicates her HER2 status as positive or negative. Approximately 15-25% of breast cancers are linked to a mutation in the HER2 gene and uncontrolled growth of the HER2 receptors and breast cells as a result, known as HER2-positive breast cancer.

There are various tests that may be used to determine HER2 status, including:

• Immunohistochemistry (IHC) test: detects excess HER2 protein in breast cancer cells. Scale ranges from 0 (negative) to 3+ (positive).
• Fluorescence in situ hybridization (FISH) test: detects excess copies of HER2 gene in breast cancer cells. The result will be either positive or negative.
• Subtraction probe technology chromogenic in situ hybridization (SPoT-Light HER2 CISH) test: detects excess copies of HER2 gene in breast cancer cells. The result will be either positive or negative.
• Inform HER2 Dual in situ hybridization (ISH) test: detects excess copies of HER2 gene in breast cancer cells. The result will be either positive or negative.

It is important to note that the accuracy of these tests is not 100% correct. Research has shown that there can be some discrepancies in the test results, which may be related to different classification systems or criteria used in different laboratories, or the area of the breast from which the sample was taken. This is most likely to occur when the HER2 status of the patient is border-line.

Targeted therapies

There are some treatments available that specifically target HER2-positive breast cancer cells, known as targeted therapies. Examples of these include:

• Trastuzumab: blocks the ability of cancer cells to receive the chemical stimuli that encourage cell growth and replication.
• Ado-trastuzumab emtansine: delivers chemotherapeutic agent emtansine directly to the affected cancer cells by combining it with trastuzumab, which has an affiliate of the cells.
• Pertuzumab: blocks the ability of cancer cells to receive the chemical stimuli that encourage cell growth and replication.
• Lapatinib: blocks certain proteins that can lead to uncontrolled cell growth.

The appropriate treatment choice will depend on the patient and characteristics of the breast cancer. These targeted therapies are often combined with other treatments for breast cancer, such as surgery, chemotherapy, radiotherapy, or hormonal therapy.

Prognosis

Traditionally, HER2-positive breast cancer has been associated with a poorer prognosis than for other types of breast cancer. This is because HER2-positive breast cancer cells tend to replicate more quickly than other types of breast cancer.

However, with the introduction of targeted treatments that can focus their action on this specific type of cancer cell, the natural history of the disease is changing. The targeted nature of the treatments has seen improved survival rates for patients, in addition to a reduced risk of side effect.

In the future, this success could be deepened with further research about the signal transduction of HER2 and the related pathways in the breast cancer cells.

References

• http://www.breastcancer.org/symptoms/diagnosis/her2
• http://www.macmillan.org.uk/cancerinformation/cancertypes/breast/aboutbreastcancer/typesandrelatedconditions/her2%20positive.aspx
• http://www.lbbc.org/learn/types-breast-cancer/her2-positive-breast-cancer
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4307801/