Moderator: Dr. Marisa Nucci
Pleomorphic rhabdomyosarcoma of the uterus
W Glenn McCluggage, M.D.
Royal Group of Hospitals Trust
Belfast, Northern Ireland
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.
Pleomorphic rhabdomyosarcoma of the uterus.
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 . A sarcomatous element is also a component of uterine
adenosarcoma and carcinosarcoma (malignant mixed Mόllerian 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 . Other examples have
been described in case reports or small series
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
. In the largest series the patient's age ranged from 35 to 87 with a mean of 65 years
. 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.
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