Malignant ectomesenchymoma (MEM) represents a heterogeneous group of
tumors, most likely originating from pluripotent primitive neural crest cells. In this report, we present an 8-month-old infant boy with an MEM on the left scrotum. Retrospective review of the incision biopsy showed the presence of a few
ganglion cells in an otherwise classic
embryonal rhabdomyosarcoma (RMS), whereas in the resection specimen after
chemotherapy the combined RMS and
ganglioneuroma components were very obvious. Cytogenetic analysis of the residual lesion showed an
abnormal karyotype, 49, XY, +2, -6, +11, +20, +mar, with a hyperploidy in a subset of cells. By fluorescence in situ hybridization analysis, the
marker chromosome was identified as originating from chromosome 6, and the
tumor cells were negative for PAX3/PAX7 disrupting translocations specific for alveolar RMS. Gains of chromosomes 2, 11, and 20, found in the current case, are a common finding in embryonal RMS. These gains probably reflect the myogenic differentiation of MEM and support the genetic link between these 2
neoplasms. In addition to the conventional cytogenetics, array comparative genomic hybridization analysis was performed on the primary and
residual tumors. The genomic profiles of both specimens were basically the same including the presence of 2 distinctive chromosome 6p21.32-p21.2 and 6p11.2 amplification regions in the primary
tumor, which vanished in the postchemotherapy specimen. The pretreatment biopsy exhibited strong expression of HMGA1 and HMGA2
proteins in immunohistochemistry, with the shift toward the loss of expression of both genes in the posttreatment tumoral tissue. This finding supports the oncogenic properties of the
HMGA family of
proteins and their role in the process of malignant transformation.