Osteoclast-like Giant Cells: Definition

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Osteoclast-like giant cells are very large cells with many nuclei that look like osteoclasts, the cells that normally break down bone. Despite the name, they can be found both inside and outside of bone. They are a type of multinucleated giant cell.

Osteoclast-like giant cells are a description of what the pathologist saw under the microscope, not a diagnosis on their own. They appear in many noncancerous conditions and some cancers. This article explains what osteoclast-like giant cells are, where they are found, and what they mean in your pathology report.

What are osteoclast-like giant cells?

Osteoclast-like giant cells form when several immune cells called macrophages fuse into one large cell. This is the same way that normal osteoclasts form. In most cases, nearby cells send signals that cause the macrophages to fuse.

In most tumors with osteoclast-like giant cells, the giant cells are not tumor cells. They are normal cells attracted to the area by the tumor. The tumor cells are usually smaller, single-nucleus cells mixed among the giant cells.

What do osteoclast-like giant cells look like under the microscope?

Under the microscope, osteoclast-like giant cells are very large, with abundant pink cytoplasm. Each one contains many nuclei, often 10 or more, scattered throughout the cell. The nuclei usually look bland, meaning they lack the abnormal features seen in cancer cells.

Osteoclast-like giant cells are different from other types of giant cells. For example, Touton giant cells have their nuclei arranged in a ring and a pale, foamy outer rim.

Where are osteoclast-like giant cells found?

Osteoclast-like giant cells are seen in many different conditions. Common examples include:

Giant cell tumor of bone. Giant cell tumor of bone is a noncancerous bone tumor that can grow into nearby bone and come back after treatment. It is made of sheets of osteoclast-like giant cells, with smaller tumor cells between them.
Tenosynovial giant cell tumor. This noncancerous tumor of joints and tendon sheaths often contains osteoclast-like giant cells. It is also called giant cell tumor of tendon sheath.
Aneurysmal bone cyst. The walls of an aneurysmal bone cyst usually contain osteoclast-like giant cells.
Reactions in bone and soft tissue. Osteoclast-like giant cells are often seen around healing fractures, areas of old bleeding, and in a bone lesion caused by overactive parathyroid glands, called a brown tumor.
Some cancers. Some carcinomas of the pancreas, breast, and bladder contain many osteoclast-like giant cells. Some sarcomas, including some osteosarcomas, can also contain them.

How are osteoclast-like giant cells identified?

A pathologist identifies osteoclast-like giant cells while examining the tissue on routine slides. No special test is needed to see them. Because they are found in so many conditions, the pathologist focuses on the other cells in the sample to make the diagnosis.

Immunohistochemistry can help. Osteoclast-like giant cells are usually positive for CD68, a marker of macrophages. Clinicians use other markers or molecular tests to identify the smaller cells around them. For example, most giant cell tumors of bone have a specific change in a gene called H3-3A that can be detected in the tumor cells.

What do osteoclast-like giant cells mean for me?

Finding osteoclast-like giant cells does not mean cancer. Their meaning depends on the final diagnosis, which your report will list separately. In many cases, they are part of a noncancerous tumor or a reaction to injury.

Questions to ask your doctor

What is the final diagnosis in my report?
Is the tumor noncancerous or cancerous?
Are the giant cells part of the tumor or a reaction to it?
Were additional tests done to identify the other cells in my sample?
Was the lesion completely removed?
Could the lesion come back after it is removed?
Do I need any further treatment or follow-up?