by Jason Wasserman MD PhD FRCPC
May 6, 2022
CD68 is a protein made by cells that contain specialized parts called lysosomes. Cells use lysosomes to grab and break down potentially harmful elements in their environment. For example, specialized immune cells called macrophages and histiocytes use lysosomes to kill bacteria. While CD68 is found mostly in immune cells, any type of cell that contains lysosomes can make CD68.
Pathologists test for CD68 to see if the cells they are seeing under the microscope are making lysosomes. Most of the time, pathologists look for lysosomes to confirm that the cells are macrophages or histiocytes. It is normal to see an increased number of macrophages or histiocytes in the tissue around an infection or in an area of inflammation. These cells contribute to the normal healing and repair process. Pathologists may also test for CD68 when examining a tumour because some types of tumours (for example granular cell tumour) are also known to make lysosomes. In this situation, CD68 is used to confirm the diagnosis and exclude other similar looking tumours.
Pathologists perform a test called immunohistochemistry to look for CD68 inside cells.
“Positive for CD68” means that the cells in the tissue sample contain lysosomes. Both normal and cancerous macrophages, as well as histiocytes, will be positive for CD68. Other types of cells, including some tumour cells that make lysosomes, will also be positive for CD68.
“Negative for CD68” means that the cells of interest in the tissue sample do not contain lysosomes. Any type of cell that does not contain lysosomes will typically be negative for CD68.
Your pathologist will combine the result of this test with other information such as the microscopic features seen on the routine hematoxylin and eosin (H&E) slide and the results of other immunohistochemistry tests before making a final diagnosis.