Spindle Cell Lipoma : RB1 Deletion
Cytogenetics: Both spindle cell and pleomorphic lipomas show rearrangements of 16q or 13q in most cases. Deletion of 13q14 region causes loss of tumor suppressor gene RB1, encoding the Rb protein. The same deletion is also found in cellular angiofibroma and mammary-type fibroblastoma. Rb immunohistochemistry has proved to be a useful tool in separating spindle cell and pleomorphic lipomas (no Rb expression) from its histologic mimics (intact Rb expression). Spindle cell and pleomorphic lipomas donít have giant marker and ring chromosomes that are seen in atypical lipomatous neoplasm/well-differentiated liposarcoma.