Macrophage and Multinucleated Giant Cell

Macrophages and multinucleated giant cells are another of the reactive cells found associated with tumors that must be correctly identified. Part of such a reactive cells may contain distinctive cytoplasmic organelles differing from those expected in tumor cells. For example, small primary lysosomes in macrophages may look like neuroendocrine granules or exocrine granules. Macrophages as part of their phagocytic function have many narrow, cell surface processes (referred to as filopodia) that can readily be misinterpreted as microvilli. Multinucleated giant cells, especially in soft tissue tumors, can be misinterpreted as osteoclasts.

Macrophage

Figure 1. Macrophage from peripheral primitive neuroectodermal tumor with the typical reniform nuclear profile and some (though not abundant) primary and secondary lysosomes (arrowheads). Also characteristic of a macrophage are the numerous slender cell surface processes (filopodia; arrows). Although the heterochromatin is not abundant, the chromatin pattern is noticeably different from that of adjacent tumor cells. X8,500.

Figure 2. Macrophage from Burkitt-type lymphoblastic lymphoma. This shows primary lysosomes (one or two of them mimicking neuroendocrine granules) and secondary (arrows) lysosomes in detail. X20,000.

Multinucleated giant cell

Figure 3. Multinucleated giant cell in an osteosarcoma. Note the darker-staining cytoplasm, and different cytoplasmic content and nuclear morphology of the giant cell compared with the spindled osteosarcoma cells (right). X5,000.