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