IHC Test for Cancer: What It Is and Why It’s Done

What is an IHC Test for Cancer?

Immunohistochemistry (IHC) is a standard laboratory technique often used to detect the specific proteins in tissue samples. These tests rely on antibodies, especially some specific molecules designed to bind to specific proteins. These are used to highlight, or ‘stain,’ some specific structures in the cells of a specific tissue. IHC tests are typically performed on the biopsy samples, which are pieces of tissue taken from the body for examination.

Why is the IHC Test done?

Performing IHC tests serves different purposes in the landscape of cancer diagnosis and treatment.

Here are some of the key reasons why it's done in patients, including:

Diagnosis of the cancer:

In some cases, it can be difficult to tell what type of cancer a patient has just by looking at the cells under a microscope. Different types of cancer might look at the cellular level, but the presence of certain types of proteins can help to identify them. The IHC test can provide clarity by recognising the tumor markers that are specific to some types of cancer.

For example: breast cancer cells may test positive for estrogen receptors (ER) or progesterone receptors (PR), which helps to classify the tumor as hormone- receptor positive, influencing the treatment approach.

Determining the origin of the metastatic cancer:

In some cases, cancer cells spread (metastasize) from one part of the body to another, and identifying the origin of the metastasis is considered to be crucial. IHC tests can help the doctors to trace the cancer back to its original site by examining the proteins that are specific to the tissue type.

For example: If the cancer has spread from the lungs to liver, an IHC test can help to determine whether these types of cells are lung cells or liver cancer cells.  

Personalized treatment: 

Some types of cancers have specific molecular markers that can be targeted with extreme precision treatments. While identifying these markers with IHC, doctors often recommend the most effective treatment options. For instance, HER2 (human epidermal growth factor receptor 2) testing for breast cancer can determine whether patients will benefit from targeted therapies like trastuzumab (Herceptin). 

Prognostic information

IHC tests can offer some important prognostic information. For example: the Ki-67 protein, which is usually associated with cell proliferation, can give more accurate details about how fast the cancer cells are growing. High Ki-67 levels might suggest a more aggressive type of cancer, while low levels could indicate a slower growing tumor. 

Predicting the treatment response:

In some cancers, such as colorectal cancer, the IHC test is used to check for mutations in proteins that affect the cancer's response to chemotherapy or other treatments. For example, performing a test for the KRA mutation can often indicate whether a patient with colorectal cancer is likely to respond to the EGFR-targeted therapies.

The benefits of IHC in cancer diagnosis and Treatment

IHC tests have several advantages that make these tests an essential tool in cancer care.

• Accuracy: By revealing a specific protein in cancer cells, IHC tests provide a more accurate cancer diagnosis, which helps to identify the exact type of cancer and its molecular profile.
• Guiding treatment: IHC test results can help identify biomarkers that allow the doctors to choose the best possible treatment for a patient.
• Personalized medicine: IHC tests help to personalise treatment strategies to the unique biology of each patient’s cancer types.
• Monitoring: These tests can be used to monitor changes happening in the cancer over time, offering accurate information about how this cancer is progressing or responding to the treatments.