Spindle Cell Lipoma : RB1 Deletion

RB1 Deletion: As discussed in the previous slide, the majority of spindle cell/pleomorphic lipomas carry deletions of chromosome 13q or entire chromosome 13 with loss of tumor suppressor gene RB1, encoding the Rb protein. Rb immunohistochemistry has proved to be a useful tool in separating spindle cell and pleomorphic lipomas (no Rb expression; see spindle tumor cells in this image) from its histologic mimics (intact Rb expression). Note the intact Rb expression in the endothelial cells as a nice internal positive control in the image.