Has your doctor ordered a biopsy for you or someone you know? A biopsy is when a small piece of tissue is removed from a lump in your body and examined. So, you may be wondering what exactly is done to that small piece of tissue in the lab. Today, we are going to talk about a very important test used in medicine today. It is called immunohistochemistry , or IHC for short among doctors.
What is IHC simply?
Simply put, IHC is a special lab test used by pathologists, doctors who specialize in diagnosing diseases, to look for signs of disease in a tissue sample.
Although this name may seem a bit long, its meaning is very easy to understand when broken down into a few words.
- Immuno: This is related to our body's immune system . You know, when we get foreign substances (viruses, bacteria, etc.) or foreign substances like cancer cells, our immune system recognizes them. We call these foreign substances antigens . So, our body makes a special type of protein to capture and destroy these antigens. They are called antibodies . Just like a key opens a lock, there is a special antibody that matches each antigen. In the IHC test, these antibodies, which are made in the lab, are used to find the antigens related to the disease in the tissue sample.
- Histo: This refers to tissue . This means that this test is performed on a piece of tissue taken from your body.
- Chemistry: This means the study of things that are small enough to be seen only with a microscope, using chemical methods.
Then, putting all of this together, IHC is a method of identifying the disease by using the concept of antibodies in our immune system, adding something like a dye to the pathogen particles (antigens) in a tissue sample, and looking at them under a microscope.
When is an IHC test performed?
IHC testing is used for many things these days. The information it provides can be a great help to your doctor in choosing the best treatment for you.
| Usage | Simple explanation |
|---|---|
| To correctly diagnose a disease | This is especially important for diagnosing cancer. It can help determine the exact type of cancer (e.g., carcinoma, melanoma). It can also help determine the origin of metastatic cancer, which is a cancer that has spread from one part of the body to another. |
| To determine the status and course of the disease | It can help you understand how serious the cancer is and how fast it is spreading. The information from this test is also important in determining the stage and grade of the cancer. Based on this information, the doctor will develop the best treatment plan. |
| To predict response to treatment | Some cancers, especially breast and prostate cancers, grow in response to hormones such as estrogen and testosterone. IHC testing can identify cancers that are sensitive to these hormones. Hormone therapy can then be given to block those hormones. |
| To monitor the success of treatments | IHC testing is sometimes used to see if the treatment is improving the disease and whether the cancer cells are disappearing. |
Additionally, IHC is also very important in research to find new drugs. It helps researchers understand the changes that occur in our cells due to disease.
How does this test work?
The basic principle of this is very simple. It's like finding the right key (antibody) for a lock (antigen).
Imagine that you have cancer cells in your tissue sample. Those cancer cells have antigens (markers) on their surface that are specific to them. What you do in the lab is use an antibody that is specifically designed to bind to that antigen.
Here's how this process works:
1. The pathologist attaches an enzyme to the selected antibody. This enzyme is like a little signal.
2. This antibody mixture is then placed on top of the prepared tissue sample.
3. If the sample contains the antigen related to that disease, the antibody we added will stick to it (just like a key fitting into a lock).
4. When it sticks like this, the enzyme attached to the antibody is activated, creating a special color in that area.
5. Finally, when viewed under a microscope, the colored areas are clearly visible. This means that there are antigens related to the disease in those areas, which means we can confirm that the disease is present.
For this result to be 100% accurate, these steps must be performed very carefully and accurately in the lab.
Preparing the sample for testing
It is very important to prepare the tissue sample properly.
- Preserve the tissue: Once removed from the body, the cells in the tissue gradually begin to die. To stop this, the tissue is "fixed" by placing it in a chemical like formalin. This keeps the tissue's structure intact.
- Ensure antigens are accessible: Sometimes, this fixing process can cause antigens to become occluded. Then, antibodies cannot attach to them. Therefore, a special process called "antigen retrieval" is used to re-expose the occluded antigens.
- Block similar structures: Sometimes our antibodies can bind to other things that are similar to the real antigen we are looking for. It's like someone else sitting in the chair reserved for the right person. To prevent this, we block similar structures in advance. Then the antibody will only bind to the right target.
Choosing the right antibodies
The pathologist must choose the right type of antibody for the antigen they are looking for. There are two main types.
| Antibody type | Specialty |
|---|---|
| Polyclonal antibodies | These are a mixture of different antibodies that can bind to different sites on the same antigen. |
| Monoclonal antibodies | These are copies of the same type, the same antibody. They only bind to one specific site on the antigen. |
Are there any limitations and drawbacks to the IHC test?
Yes, like all tests, this one has some limitations.
One of the biggest challenges is that there are no globally accepted standard guidelines for each step of the IHC test. Therefore, the methods and chemicals used in different labs can vary slightly, leading to some variation in results.
In addition, sometimes the results can be wrong.
| Error in the result | Meaning |
|---|---|
| False-positive | A result indicating that the antigen relevant to the disease is present even though the sample is not present. |
| False-negative | Even though the sample contains the antigen related to the disease, the result is negative. |
To prevent things like this, good labs have quality control procedures. That is, before doing the actual test, they test the antibody on a tissue that we know has the disease to make sure it works properly.
Is IHC the same as a biopsy?
No, but there is a big connection between the two.
Simply put, a biopsy is the process of removing a piece of tissue from your body. IHC is a method of examining that piece of tissue in a lab. In other words, IHC is a test that is done after a biopsy.
IHC is truly a marvel of medicine. It allows doctors to see signs of disease that are not visible to the naked eye. The information obtained from this test is invaluable in fighting diseases like cancer and choosing the right treatment.
Take-Home Message
- Immunohistochemistry (IHC) is nothing to be afraid of. It's a special test done in a lab on a small piece of tissue taken from your body.
- This test can provide a lot of important information (such as the type of cancer and its severity), especially about diseases like cancer.
- This involves finding special markers (antigens) on diseased cells, adding something like a dye to them, and looking at them under a microscope.
- The report from the IHC test will greatly help your doctor choose the most suitable and effective treatment for you.
- If you have any questions about this test, never be afraid to talk to your doctor about it openly.
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