18 June 2008
PRIMARY PLEOMORPHIC RHABDOMYOSARCOMA OF TRUNK IN AN ADOLESCENT
Rhabdomyosarcoma (RMS) is the most common type of soft-tissue sarcoma in children and adolescents, accounting for approximately 5% of all paediatric cancers and more than half of all soft-tissue sarcomas. RMS of the trunk is rare, comprising 4–7% of all RMS in the Intergroup Rhabdomyosarcoma Study (IRS) report.1 Truncal RMS is associated with a poor prognosis. Because the non-specific and somewhat unremarkable initial symptoms make early diagnosis difficult, the tumours enlarge and are often detected at advanced stages. Pleomorphic RMS was first described by Stout in 1946.2 Later studies reported that pleomorphic RMS was rare and occurred predominantly in adults. Herein, we describe one case of truncal pleomorphic RMS.
A 14-year-old female was referred to our hospital with an 8-month history of a painless swelling on the left-sided posterior back. The patient had been brought to another local hospital 1 month earlier and received incisional biopsy, but no definite diagnosis was obtained. The patient's medical history was unremarkable. Physical examination revealed a diffusely enlarged, non-tender and hard mass. Routine blood tests were normal. The patient's serum levels of CEA, CA125 and CA19-9 were within normal limits, with the exception of an elevated serum NSE level of 63.59 ng/mL (reference range, <15 ng/mL). The paraffin-embedded tissue was analysed, photomicrograph noted spindle and pleomorphic tumour cells, and immunohistochemistry showed strong and diffuse positive stain for smooth muscle actin, desmin, myogenin, sarcomeric actin and negative for CD10, S-100 protein. All findings were in agreement with the diagnosis of a pleomorphic RMS. Magnetic resonance imaging (MRI) revealed a 15.5 cm × 10.8 cm × 6.5 cm extensive soft-tissue tumour, the mass sited primarily in the paraspinal area, protruded into the spinal extradural space. The chest computed tomography, abdominal Doppler ultrasonography and radionuclide bone scan were all negative for metastasis. The patient was considered to have a group III RMS, according to IRS criteria, and subsequently underwent chemotherapy and external radiotherapy. A combination chemotherapy of vincristine, dactinomycin, and cyclophosphamide was given at three-weekly intervals, high-dose radiotherapy was added to the patient's chemotherapy regimen at week 3 (54 Gy at 2 Gy/fraction), and hypoxic radiosensitiser sodium glycididazole (800 mg/m2) was used 30 min prior to irradiation. She tolerated the treatment well, no adverse side effects were reported, except for skin pigmentation.
RMS is a malignant neoplasm arising from embryonal mesenchyma and is the most common soft-tissue sarcoma during the first two decades of life. This disease follows a bimodal distribution with peak incidences between 2 and 6 years and again between 10 and 18 years of age; however, approximately two-thirds of cases are diagnosed in children younger than 6 years of age.3
On light microscopy, identification of cross-striations or characteristic rhabdomyoblasts may shed light onto the tumour's skeletal myogenic lineage. Immunohistochemistry is invaluable in the diagnosis of RMS, staining for muscle-specific myosin and actin, desmin, myoglobin, z-band protein and MyoD, myogenin can support the diagnosis of RMS. Three general pathologic types of RMS have been described: embryonal, alveolar and pleomorphic. Most frequent is the embryonal subtype, accounting for 70–75% of all RMS, followed by the alveolar (20–25%) and pleomorphic differentiation (5%). Pleomorphic RMS typically presents in adults ≥45 years of age. However, the pleomorphic subtype is extremely rare in children, only 11 of 1626 cases (0.7%) entered on IRS-I and II protocols were pleomorphic.4
Overall, approximately 40% of RMS occurs in the head and neck region; RMS in the trunk is rare. Truncal sites include the chest wall, paraspinal area and abdominal wall. Of these subsites, the most common location is the chest wall; RMS arising from the paraspinal area only comprises 3.3% of all cases. These lesions tend to be >5 cm at diagnosis in close proximity to the vertebral column and spinal canal.5,6 Surgical resection is often difficult when the paraspinal tumours spread along anatomical structures such as neurovascular bundles and fascial sheaths, and this contributes to the inferior outcomes.
Primary excision of RMS should be attempted only when the surgeon thinks a complete resection can be achieved without important functional or cosmetic consequences. In most cases, therefore, primary surgery is limited to biopsy alone. The important role of radiotherapy in the management of RMS is well recognised; radiotherapy is important for local tumour control and survival.3 After biopsy or resection, the majority of children requiring radiotherapy are Group II (microscopic residual disease) or Group III (gross residual disease). In terms of local control, conventional radiation therapy is generally used for patients with gross disease. A randomised trial compared 50.4 Gy in 28 fractions with a hyperfractionated arm of 59.4 Gy in 54 fractions (1.1 Gy twice daily). No advantage was demonstrated in local control between conventional and hyperfractionated schedule.7 RMS is a chemosensitive tumour. The most widely used chemotherapy regimen includes vincristine, dactinomycin and cyclophosphamide, which has been the gold standard for combination chemotherapy in the treatment of most cases of RMS.
In conclusion, pleomorphic RMS is rare but exists in childhood. More clinical trials and a better understanding of the molecular biology driving RMS tumour behaviour may assist with customised clinical therapies that will improve outcome in patients diagnosed with truncal RMS.