Collagen is a strong, fiber-forming protein that holds the body’s tissues together. It is the body’s most common protein. Collagen gives strength to the skin, bones, tendons, ligaments, and the walls of blood vessels and organs. Cells called fibroblasts make it.
Collagen is a normal part of almost every tissue sample, so its presence is not a diagnosis. Pathology reports mention collagen when there is more of it than usual, when it looks abnormal, or when it forms part of a tumor. This article explains what collagen is, what it looks like under the microscope, and why it may be mentioned in your report.
What does collagen do?
Collagen fibers work like the steel cables in a building. They give tissues strength and hold cells and structures in place. Collagen is part of the stroma, the supporting tissue that surrounds an organ’s working cells
There are many types of collagen. Some form thick fibers in the skin, bone, and tendons. Others form thin sheets beneath the lining of organs. When tissue is injured, fibroblasts make new collagen to repair the damage. This is how a scar forms.
What does collagen look like under the microscope?
On routine hematoxylin and eosin (H&E) slides, collagen appears as pink fibers or bands. Mature collagen is dense and contains few cells. Newer collagen is looser and contains more fibroblasts.
When the pathologist needs to see collagen more clearly, they may use a special stain called a trichrome stain. This stain colors collagen blue or green, making it easier to measure how much scar tissue is present.
Why is collagen mentioned in a pathology report?
Pathology reports mention collagen for several reasons:
- Scarring. An increase in collagen after injury or long-term inflammation is called fibrosis. Fibrosis is described in many organs, such as the liver, lungs, and kidneys.
- Reaction to a tumor. Some cancers cause the surrounding tissue to make dense collagen. This reaction is called desmoplasia, and it often makes a tumor feel hard.
- Thick or overgrown scars. In a keloid scar, the body makes too much collagen, forming thick, glassy bands that extend beyond the original wound.
- Collagen in the lining of the bowel. In collagenous colitis, a thick band of collagen forms under the colon lining. This finding helps confirm the diagnosis in people with long-lasting watery diarrhea.
- Tumors that make collagen. Many spindle-cell tumors, such as a dermatofibroma, contain collagen made by the tumor cells.
Your report may describe collagen as “dense,” “hyalinized,” or “sclerotic.” These words mean the collagen is thick and glassy, usually because it has been present for a long time.
Some inherited conditions affect how the body makes collagen. Doctors usually diagnose these conditions with genetic testing rather than by examining tissue under a microscope.
Questions to ask your doctor
- Why does my report mention collagen?
- Is the collagen part of a scar, a reaction to a tumor, or the tumor itself?
- Does my report describe fibrosis, and how much is present?
- Was a trichrome or other special stain used?
- What is the final diagnosis in my report?
- Does this finding change my treatment or follow-up?
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