ABSTRACT
BACKGROUND: Rhabdomyosarcoma (RMS) is an aggressive malignancy,
and 20% of children present with metastases at diagnosis. Patients
presenting with disseminated disease very occasionally have no clear
evidence of a primary tumor mass. Since these patients have rarely been
investigated, we report on a series of patients with RMS and unknown
primary tumor site registered in the MTS 2008 protocol (October 2008 -
December 2016) coordinated by the European pediatric Soft tissue sarcoma
Study Group.
METHODS:Patients were administered 9 cycles of induction chemotherapy, and 48
weeks of maintenance chemotherapy. Surgery and/or radiotherapy was
planned after the first assessment of tumor response, and implemented
after six cycles of chemotherapy. If feasible, radiotherapy to all sites
of metastasis was recommended.
RESULTS: We identified 10 patients with RMS and unknown primary
site, most of them adolescents (median age 15.8 years, range 4.6-20.4).
Nine had fusion-positive alveolar RMS. Multiple organ involvement was
identified in 7 patients, 2 only had bone marrow disease, and 1 only had
leptomeningeal dissemination. All patients were given chemotherapy, 4
were irradiated, and none had surgery. Three patients underwent
allogeneic bone marrow transplantation. At the time of this analysis,
only 2 patients are alive in complete remission: 1 had received
radiotherapy; and 1 had a bone marrow transplant.
CONCLUSIONS: RMS with unknown primary tumor occurs mainly in
adolescents and is typically fusion-positive alveolar. Radiotherapy may
be important, but survival is poor and patients should be offered
enrollment in investigational trials.