Rhabdomyosarcoma is the most common pediatric soft tissue malignancy. Two major subtypes, alveolar rhabdomyosarcoma and embryonal rhabdomyosarcoma, constitute 20 and 60% of all cases, respectively. Approximately 80% of alveolar rhabdomyosarcoma carry two signature chromosomal translocations, t(2;13)(q35;q14) resulting in PAX3-FOXO1 fusion, and t(1;13)(p36;q14) resulting in PAX7-FOXO1 fusion. Whether the remaining cases are truly negative for gene fusion has been questioned. We are reporting the case of a 9-month-old girl with a metastatic neck mass diagnosed histologically as solid variant alveolar rhabdomyosarcoma. Chromosome analysis showed a t(8;13;9)(p11.2;q14;9q32) three-way translocation as the sole clonal aberration. Fluorescent in situ hybridization (FISH) demonstrated a rearrangement at the FOXO1 locus and an amplification of its centromeric region. Single-nucleotide polymorphism-based microarray analysis illustrated a co-amplification of the FOXO1 gene at 13q14 and the FGFR1 gene at 8p12p11.2, suggesting formation and amplification of a chimerical FOXO1-FGFR1 gene. This is the first report to identify a novel fusion partner FGFR1 for the known anchor gene FOXO1 in alveolar rhabdomyosarcoma. Rhabdomyosarcoma accounts for 4-10% of pediatric malignancies. Four pathological subtypes have been traditionally defined: alveolar rhabdomyosarcoma, embryonal rhabdomyosarcoma, botyroid rhabdomyosarcoma, and pleiomorphic rhabdomyosarcoma. 1,2 Alveolar rhabdomyosarcoma and embryonal rhabdomyosarcoma have distinct clinical manifestations, biological behavior, genetic alterations, and account for B20 and B60% of all cases, respectively. 1 Alveolar rhabdomyosarcoma is most often seen in older children and is associated with a poor outcome, while embryonal rhabdomyosarcoma primarily occurs in children younger than 4 years of age and is usually associated with a better prognosis. 2 A rare solid variant of alveolar rhabdomyosarcoma has been described that is often morphologically indistinguishable from poorly differentiated embryonal rhabdomyosarcoma and may be confused with other 'small, round, blue cell tumors'. 3 A study of a large pediatric cohort of 171 patients with rhabdomyosarcoma by the children's oncology group (COG) has demonstrated the role of genetics in the development of rhabdomyosarcoma. 4 In the subtype of alveolar rhabdomyosarcoma, approximately 80% of cases harbored two signature chromosomal translocations, t(2;13)(q35;q14) in 60%, and t(1;13) (p36;q14) in 20% of cases. These translocations resulted in the formation and overexpression of chimerical genes PAX3-FOXO1

The ossifying renal tumor of infancy is a rare neoplasm diagnosed in the first 2 years of life, predominantly in boys. The neoplasm is primarily characterized by the presence of a large ossifying component. Its most common mode of presentation is hematuria, and it has a uniformly benign behavior. The karyotypic makeup of the process has not been reported. Thus, a study was undertaken and it allowed demonstration of clonal trisomy 4, which was confirmed by the fluorescent in-situ hybridization-probing of two additional archival formalin-fixed, paraffin-imbedded similar tumors. On the basis of the findings in these three cases, it seems that clonal trisomy 4 may be considered as a characteristic of the tumor, which makes it distinct from any other infantile renal tumor.

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Chondromyxoid fibroma is a rare benign tumor accounting for 1-2% of primary bone tumors. Most of the patients are young males in the 2nd and 3rd decades of life. Metaphyses of long bones are predominantly affected. The histology of this tumor is well established, but its genetic mechanism remains poorly characterized. To our knowledge, only 22 abnormal cytogenetic analyses have been reported, and all contained diploidy or near-diploidy karyograms as their primary event, and inv(6)(p25)(q13) and rearrangements involving regions 6p23-25, 6q12-15, and 6q23-27 constituted a recurrent observation. In this report, a pseudotetraploidy tumor clone with multiple numerical and structural aberrations involving 6p23 as well as other chromosomal loci was identified in a chondromyxoid fibroma from the metaphysis of the left fibula of an 18-year-old male, which has not been reported. The finding may relate to the atypical-looking large cells often seen in this benign tumor.