[Proliferative myositis]

We report on a 42-year-old woman showing a rapidly growing tumor on her left flank; it was removed by surgery. Histological examination revealed the typical picture of proliferative myositis. Since the clinical symptoms of this disease are nonspecific, the diagnosis always depends on histological evidence. Despite its rapid growth and its cellular pleomorphism, proliferative myositis is a reactive process and has to be differentiated histologically from sarcoma of the soft tissue.