Maisa Yoshimoto

The breakage–fusion–bridge (BFB) cycle as a mechanism for generating genetic heterogeneity in osteosarcoma

Osteosarcoma (OS) is characterized by chromosomal instability and high copy number gene amplification. The breakage–fusion–bridge (BFB) cycle is a well-established mechanism of genome instability in tumors and in vitro models used to study the origins of complex chromosomal rearrangements and cancer genome amplification. To determine whether the BFB cycle could be increasing the de novo rate of formation of cytogenetic aberrations in OS, the frequency of anaphase bridge configurations and dicentric chromosomes in four OS cell lines was quantified. An increased level of anaphase bridges and dicentrics was observed in all the OS cell lines. There was also a strong association between the frequencies of anaphase bridges, dicentrics, centrosomal anomalies, and multipolar mitotic figures in all the OS cell lines, indicating a possible link in the mechanisms that led to the structural and numerical instabilities observed in OS. In summary, this study has provided strong support for the role of the BFB cycle in generating the extensive structural chromosome aberrations, as well as cell-to-cell cytogenetic variation observed in OS, thus conferring the genetic diversity for OS tumor progression.

Detection of ERG gene rearrangements and PTEN deletions in unsuspected prostate cancer of the transition zone

To assess the incidence of ERG rearrangements and PTEN deletions in a group of prognostically favorable PCA tumors of the transition zone (TZ). We interrogated 54 unsuspected PCA tumors using fluorescence in-situ hybridization for ERG rearrangements and PTEN deletions. ERG rearrangements were detected in 6/47 (12.7%) cases with 4/6 (66%) occurring by deletion. PTEN deletions were detected in 9/47 (19.1%) cases with only 3/47 (6.4%) having both PTEN losses and ERG rearrangements (p = 0.07). Only ERG rearrangements were associated with higher tumor volume >5% (p = 0.04); PTEN deletions showed similar trends (p = 0.06). None of the markers showed association with Gleason score. In conclusion, although TZ and peripheral zone tumors share similar molecular etiologies, they exhibit differences in the rates of ERG and PTEN aberrations. The differences of ERG and /or PTEN genetic aberrations in TZ tumors may point toward a subset of tumors with adverse behavior. Additional studies implementing ERG and PTEN tissue-based FISH assays in tumors of the TZ are warranted to substantiate the potential clinical value of these biomarkers in the management of men with incidental PCA.

MYCN Gene Amplification: Identification of Cell Populations Containing Double Minutes and Homogeneously Staining Regions in Neuroblastoma Tumors

Neuroblastoma is the second most common solid tumor occurring in children. Amplification of the MYCN oncogene is associated with poor prognosis. To identify neuroblastoma tumors with MYCN amplification, we studied the number of copies of MYCN in interphase cells by fluorescence in situ hybridization in 20 neuroblastoma patients. MYCN amplification appeared in 7 tumor specimens. Interphase and metaphase studies showed a tumor cell population with both forms of amplification, double minutes and homogeneously staining regions, in two patients. These patients showed a smaller tumor cell subpopulation with the presence of more than one homogeneously staining region, suggesting that gene amplification was undergoing karyotype evolution.

Myelodysplastic syndrome in childhood: report of two cases with deletion of chromosome 4 and the Philadelphia chromosome

We report two pediatric patients with unclassified myelodysplastic syndrome (MDS) by the French-American-British (FAB) group. Both cases had clinical and hematological peculiarities, which had not been described yet. The cytogenetic alterations were 4q deletion and the Philadelphia (Ph) chromosome which appeared at different moments of the disease. One patient showed the Ph chromosome at disease transformation and the other at diagnosis. The different breakpoints at 4q and the presence of Ph could be a marker of this form of MDS. The association of clinical and hematological findings suggests the possibility of a new group of pediatric MDS.