This page was reviewed under our medical and editorial policy by
Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix
This page was reviewed on September 25, 2022.
Immunohistochemistry (IHC) is a diagnostic technique conducted in a laboratory. It involves performing special tests on the patient's biopsy tissue sample to help diagnose disease more precisely. IHC helps the care team distinguish between different types and subtypes of a disease by identifying specific molecules within cells, known as markers.
Immunohistochemistry is particularly useful in diagnosing certain types of cancer, providing the care team with a wealth of information about the disease to help determine treatment, such as:
Immunohistochemistry may help provide these answers.
To perform an IHC test, the care team must collect a tissue sample. The procedure to remove an abnormal or cancerous specimen is called a biopsy. Methods range from needle biopsies, which involve inserting a needle into the tumor, to excisional biopsies, which remove the entire tumor. The method used depends on individual circumstances, including the type of cancer and its location.
All biopsy types involve removing bodily tissue and taking it to a laboratory, where a pathologist who specializes in diagnosing diseases will examine the sample under a microscope. To determine whether or not the specimen is cancerous, the pathologist usually only needs to examine the cells and perform standard tests called stains, which use colored substances (dyes) to highlight cancer cells.
It may be difficult to differentiate cancer cells from healthy ones based only on their appearance and routine tests. When these methods aren’t enough to make a diagnosis, the care team may turn to IHC.
Immunohistochemistry reveals more than a standard biopsy test. It enables pathologists to determine the exact type and subtype of cancer by looking for unique tumor markers within cancer cells. Markers are identified using antibodies, a type of protein that locates and binds with antigens (which are the markers found on cells). Antigens are like cellular locks and antibodies are like keys—unique antibodies fit perfectly within their respective antigens.
More than 400 unique antibodies can be used in IHC tests. When an antibody recognizes and binds to corresponding antigen in the sample, a colored dye is activated, indicating to the pathologist that the sample contains a particular type of cell that may help determine the exact type of cancer.
IHC tests are helpful in many different circumstances, but these tests aren’t often part of the standard diagnostic process for most cancer types. For the most part, IHC tests are only ordered after a pathologist has reviewed the results of more routine tests.
Pathologists diagnose most cancers just by looking at a biopsy sample under a microscope and using stains. However, if the analysis is more complex and requires checking for more specific characteristics to make a diagnosis, the pathologist may turn to IHC tests.
The doctor and a pathologist typically determine whether or not immunohistochemistry is necessary on a case-by-case basis.
However, IHC tests are routinely used to help diagnose most types of breast cancer, including:
In patients with breast cancer, immunohistochemistry is used to test for the conditions listed below.
Hormone receptor status: IHC tests may detect the presence or absence of hormone receptors on breast cancer cells. This knowledge informs how the cancer may be treated, as breast cancers that carry these receptors can be treated with hormone therapy drugs.
HER2 status: IHC tests may check for HER2 receptors to determine whether breast cancer is HER2-positive or HER2-negative. If these receptors are found, the cancer is HER2-positive, which indicates that it’s likely to be fast-growing and may be treated by targeted therapy drugs that block the effects of the HER2 proteins responsible for fueling the cancer’s growth.
Another routine use of IHC testing is for Lynch syndrome, an inherited condition that may cause cancer or increase one’s risk of developing cancer. Lynch syndrome is most often linked to colorectal cancer, but it may also raise the risk for developing cancer in the uterus, stomach, liver, kidney and brain. Doctors may recommend using IHC to check for markers of Lynch syndrome in women who develop endometrial cancer, or anyone diagnosed with colorectal cancer before age 70.
For other cancer types, IHC testing may be warranted under certain circumstances. These include the following cancer types.
Gastrointestinal cancer: Some gastric cancers are linked to autoimmune diseases or bacterial strains, such as H. pylori. IHC tests may help inform treatment by determining whether these or other factors may be responsible for causing the cancer. IHC tests can also help differentiate between types of gastrointestinal cancer.
Prostate cancer: Some prostate cancers are difficult to diagnose using standard tests. Numerous antibodies may be used in IHC tests to learn more about the cancer, although performing these tests isn’t always necessary. IHC tests are more likely to be used if standard tests reveal mixed findings.
Lung cancer: After other tests confirm a lung cancer diagnosis, IHC tests may be necessary to define the type of lung cancer. For example, a pathologist will often need to use IHC to check for specific antigens to establish a case of non-small cell lung cancer.
Lymphoma: It may be difficult for a pathologist to recognize whether swollen lymph nodes are caused by an infection or cancer such as lymphoma. With IHC tests, the pathologist is able to test the white blood cells causing the swelling to see whether they carry cancer-indicating antigens. IHC tests may also help distinguish between different lymphoma types.
Other cancers that may sometimes need IHC testing include those of the female reproductive system, bladder and kidney. However, many other circumstances warrant using the IHC method. The decision to use IHC tests is based on careful consideration of individual factors.
This type of testing is an additional step performed on the patient's biopsy sample, so he or she won't need to prepare specifically for IHC. It is necessary to prepare for a biopsy, however.
Biopsy types vary significantly, ranging from a quick procedure performed in the doctor’s office to an invasive surgery that may come with risks. The care team provides instructions to help the patient prepare and let him or her know what to expect. For example, if the patient needs general anesthesia, he or she may be told not to eat or drink for a certain period of time leading up to the biopsy and may need someone to drive home afterward.
Before or after a biopsy, the care team may tell the patient whether IHC testing is necessary or important for a more precise diagnosis and treatment plan. If the patient isn't sure, ask the doctor which lab tests were ordered. The patient may also want to ask whether insurance covers these tests. Insurance may cover IHC testing for certain reasons but not for others.
After a biopsy procedure, the tissue is taken to a laboratory for a pathologist to examine with and without a microscope. The tissue sample may be sliced into thin pieces for microscopic examination. The slices are typically also dipped in colorful stains (dyes) to help the pathologist observe the cells and differentiate between cell types.
For an IHC test, the pathologist starts by considering the type of cancer suggested by previous tests and then selects an antibody (or several) that might help answer the remaining questions.
For example, if the sample is known to contain breast cancer cells but the pathologist needs to find out if the cells are hormone receptor-positive, he or she will use an estrogen or progesterone antibody that is known to bind with these hormone receptors. Along with the antibody, the pathologist may add chemicals or dyes to the solution. The dyes change the color of cells that contain hormone receptors, making them easily identifiable. The pathologist will then dip a slice of the sample into the antibody solution and place it under the microscope to examine.
Once the analysis is complete, a pathology report will be prepared to summarize the diagnosis and other relevant information. It may take about two to 10 days for results to be finalized and presented to the patient after a biopsy procedure. The diagnostic process may be longer or shorter, depending on the number of tests performed and their complexity. IHC tests typically only take one day longer than routine tests. More complicated analyses, such as flow cytometry, tend to delay the process further.
Once the patient receives his or her pathology report, it's important to look it over and take note of any questions or concerns. The doctor may go through the report in detail with the patient.
The benefit of IHC testing is that, when necessary, it allows the care team to gain a more precise understanding of the cancer and how best to treat it. However, these tests aren’t 100 percent accurate. Misdiagnosis of any sort is harmful, with false-positives resulting in unnecessary treatment and trauma, and false-negatives leading to potentially detrimental treatment delays.
The rate of false-positives and false-negatives vary significantly with an IHC. Numerous factors may influence the accuracy of these tests, including:
IHC test kits are regulated by the U.S. Food and Drug Administration. All test manufacturers must present data on their accuracy in repeated attempts and against other methods. Pathologists are also encouraged to regularly validate their own IHC systems to ensure that they are reporting accurate results.
While a cancer misdiagnosis can occur, systems in place are designed to help avoid this, such as requiring a second pathologist to review findings (in most accredited labs) and having a team of doctors and pathologists work together to interpret the results.