Immunohistochemistry (IHC) is a special test used by pathologists to detect specific molecules on cells.
When a tissue sample such as a lymph node biopsy is passed to a lab to be examined for disease, there are several details that cannot be determined easily.
Several diseases or disease sub-types may look alike or appear to have similar size cells under a microscope but have different behaviors and different treatments. One way to differentiate them is to detect specific molecules on these cells that act as markers.
Immunohistochemistry is a technique that uses antibodies—matching molecules—that can seek out, identify and attach themselves to these markers on cells. The antibodies themselves are designed to work with tags that can be detected or seen under a microscope, such as fluorescent staining, which helps to make a precise identification.
IHC has found numerous applications in medicine, especially in cancer diagnosis. Lymphomas are among the cancers most dependent on IHC for correct diagnosis and treatment decisions.
More on Immunohistochemistry
Some aspects of the disease can be readily seen by studying individual cells and their appearance, including the appearance of the nucleus, certain cellular proteins, and the shape or “normal anatomy” of the cell, which is called the cell’s morphology. Other aspects of disease stand out to the observer only when the suspect cells are seen in the context of “the whole neighborhood” of cells.
Other aspects require some sort of analysis at the molecular level—in other words, doctors need to know about particular gene products—the expression of certain genes into proteins, or markers that can be detected with antibodies.
Sometimes immunohistochemistry is helpful not only to identify the particular kind of lymphoma but also to help shape a prognosis, based on markers that are associated with a more slow-growing behavior vs. a more aggressive type.
IHC for Lymphomas
Lymphomas are considered malignancies of lymphocytes that have stopped in differing stages of development or differentiation, and the use of IHC with various antibodies in a “panel” helps to identify the specific lineage and developmental stage of the lymphoma.
A panel of different antibodies is used to see which markers are present on the lymphocytes. These markers often start with the letters CD. For instance, B-cell markers (CD20 and CD79a), T-cell markers (CD3 and CD5), and other markers like CD23, bcl-2, CD10, cyclinD1, CD15, CD30, ALK-1, CD138 may be used in various blood cancers or hematologic malignancies.
Consider follicular lymphoma (FL) in a bit more depth as an example of other things that can be done with IHC. FL is the second most common subtype of non-Hodgkin’s lymphoma—diffuse large B-cell lymphoma (DLBCL) is the most common. FL is also an example of what is known as an indolent lymphoma, meaning it’s a cancer characterized by slower growth and a long survival time, even without therapy. There are quite a number of different treatment options for FL, but the disease can in some ways be inconsistent from person to person.
There are prognostic indices, such as the International Prognostic Index and, more specifically, the Follicular Lymphoma International Prognostic Index (FLIPI) that can help give a picture of what kind of FL you are dealing with, and how it might behave. IHC testing of the lymphoma and its “microenvironment” was studied and two distinct classes of immune cells were found to correlate with different clinical behaviors, according to a 2006 study published in the Journal of Clinical Oncology.