Pleomorphic rhabdomyosarcoma of the uterus W Glenn McCluggage, M.D. Royal Group of Hospitals Trust Belfast, Northern Ireland

Clinical History: A 67 year old woman presented with postmenopausal bleeding and an abdominal mass was discovered on clinical examination. Hysterectomy, bilateral salpingo-oophorectomy and debulking of abdominal tumour was done. Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Diagnosis: Pleomorphic rhabdomyosarcoma of the uterus. Commentary: The most common histological subtype of uterine sarcoma is leiomyosarcoma followed by endometrial stromal sarcoma. There is also a group of high grade uterine sarcomas in which there is no definite evidence of smooth muscle or endometrial stromal differentiation morphologically or immunohistochemically. These are designated as undifferentiated endometrial or uterine sarcoma in the recent WHO classification [1]. A sarcomatous element is also a component of uterine adenosarcoma and carcinosarcoma (malignant mixed Müllerian tumour). Pure uterine sarcomas other than those listed are extremely uncommon. They are categorised as mesenchymal tumours composed of heterologous elements in the WHO classification. Other tumours in this category which have been described in the uterus include rhabdomyosarcoma, liposarcoma, malignant fibrous histiocytoma, angiosarcoma, chondrosarcoma, osteosarcoma and alveolar soft part sarcoma. There are three main morphological subtypes of rhabdomyosarcoma, namely embryonal, alveolar and pleomorphic. All three subtypes are extremely rare but have been described in the uterus. The largest published series of uterine pleomorphic rhabdomyosarcoma is 8 cases [2]. Other examples have been described in case reports or small series [3, 4, 5]. Many of the older reported cases did not have confirmatory immunohistochemistry and may not have been adequately sampled. It is possible that some of these represent rhabdomyosarcomatous overgrowth in an adenosarcoma or carcinosarcoma and others may simply represent undifferentiated sarcomas. The present case has been extensively sampled. No malignant epithelial elements were identified, excluding a carcinosarcoma. Although a few benign glandular elements were present, these were located towards the luminal surface of the tumour and are considered to represent entrapped residual endometrial type glands and not the glandular component of an adenosarcoma. Adenosarcomas are generally characterised by broad "leaf like" or "club like" projections. All uterine pure pleomorphic rhabdomyosarcomas should be extensively sampled in order to exclude sarcomatous overgrowth in a carcinosarcoma or adenosarcoma. Immunohistochemical support is necessary for a definitive diagnosis of rhabdomyosarcoma. Desmin is a global marker of muscle and does not help distinguish between a rhabdomyosarcoma and a leiomyosarcoma, a distinction that may be difficult morphologically. Alpha smooth muscle actin (a marker of smooth muscle) is usually negative in rhabdomyosarcoma while sarcomeric actin, myoglobin and myo D1 (skeletal muscle markers) are usually positive, albeit sometimes focally so. Electron microscopy may also be of value in demonstrating skeletal muscle differentiation. Most pleomorphic rhabdomyosarcomas of the uterus occur in elderly postmenopausal patients [2]. In the largest series the patient's age ranged from 35 to 87 with a mean of 65 years [2]. Pleomorphic rhabdomyosarcomas are highly malignant neoplasms, generally behaving in a very aggressive manner with frequent extrauterine spread at presentation. The overall outlook is poor with few patients surviving beyond 2 years. Optimal treatment is surgical debulking followed by adjuvant chemotherapy or radiotherapy. There are at least two possible theories regarding the histogenesis of uterine pleomorphic rhabdomyosarcoma. The neoplasm could arise from an uncommitted mesenchymal cell that undergoes rhabdomyoblastic differentiation. An alternative theory is that these neoplasms represent sarcomatous overgrowth in a carcinosarcoma or adenosarcoma. The predominant occurrence of pleomorphic rhabdomyosarcoma in elderly postmenopausal patients (similar to that of uterine carcinosarcoma) may support the later theory. References Tavassoli FA, Devilee P. World Health Organisation Classification of Tumours. Pathology and Genetics. Tumours of the Breast and Female Genital Organs. Lyon : IARC Press. 2003. Ordi J, Stamatokos MD, Tavassoli FA. Pure pleomorphic rhabdomyosarcomas of the uterus. Int J Gynecol Pathol 1997 : 16 : 369 – 377 McCluggage WG, Lioe TF, McClelland HR, Lamki H. Rhabdomyosarcoma of the uterus : Report of two cases, including one of the spindle cell variant. Int J Gynecol Cancer 2002 : 12 : 128 – 132 Jaworski RC, Rencoret RH, Moir DH. Pleomorphic rhabdomyosarcoma of the uterus. Case report with a review of the literature. Br J Obstet Gynaecol 1984 : 91 : 1269 – 1273 Holcomb K, Francis M, Ruiz J, Abulafia O, Matthews RP, Leek YC. Pleomorphic rhabdomyosarcoma of the uterus in a postmenopausal woman with elevated serum CA125. Gynecol Oncol 1999 : 74 : 499 – 501