FULL TEXT
Rhabdomyosarcoma (RMS) is an aggressive malignancy and the most common soft tissue sarcoma in childhood. It can arise from any part of the body, but the commonest sites are the head-neck region (35-40%), genito-urinary tract (20%), and limbs and trunk (20%). Two main histological subtypes are recognized: embryonal RMS (75-80% of cases), and the more aggressive alveolar RMS (20-30%), characterized by the PAX3/7-FOXO1 translocation, which often presents as metastatic at onset. At diagnosis, approximately 20% of children have distant metastases, the most frequent sites being the lungs, bone marrow, bones, and distant lymph nodes. The survival rate for these patients remains unsatisfactory, and less than 30% of patients are cured (1,2).
In a few cases, patients present with disseminated disease, but no evidence of a primary tumor mass, sometimes mimicking other cancers such as acute lymphoblastic leukemia. These cases of RMS with unknown primary tumor site have rarely been investigated, and only a few series and case reports are available in the literature (9-24). A common North American-European analysis on metastatic RMS patients included 12 patients with no evident primary tumor site, whose 3-year event-free survival (EFS) was reportedly 8% (2).
To contribute further information on this rare condition, we report a series of patients with metastatic RMS with unknown primary tumor site registered in the MTS 2008 protocol coordinated by the European pediatric Soft tissue sarcoma Study Group (EpSSG).