Intratumoral Patterns of Clonal Evolution in Meningiomas as Defined by Multicolor Interphase Fluorescence in Situ Hybridization (FISH)

Abstract

Meningiomas are cytogenetically heterogeneous tumors in which chromosome gains and losses frequently occur. Based on the intertumoral cytogenetic heterogeneity of meningiomas, hypothetical models of clonal evolution have been proposed in these tumors which have never been confirmed at the intratumoral cell level. The aim of this study was to establish the intratumoral patterns of clonal evolution associated with chromosomal instability in individual patients as a way to establish tumor progression pathways in meningiomas and their relationship with tumor histopathology and behavior. A total of 125 meningioma patients were analyzed at diagnosis. In all cases, multicolor interphase fluorescence in situ hybridization (iFISH) studies were performed on fresh tumor samples for the detection of quantitative abnormalities for 11 different chromosomes. In addition, overall tumor cell DNA content was measured in parallel by flow cytometry. iFISH studies were also performed in parallel on tissue sections in a subset of 30 patients. FISH studies showed that 56 (45%) of the 125 cases analyzed had a single tumor cell clone, all these cases corresponding to histologically benign grade I tumors. In the remaining cases (55%) more than one tumor cell clone was identified: two in 45 cases (36%), three in 19 (15%), and four or more clones in five cases (4%). Overall, flow cytometric analysis of cell DNA contents showed the presence of DNA aneuploidy in 44 of these cases (35%), 30% corresponding to DNA hyperdiploid and 5% to hypodiploid cases; from the DNA aneuploid cases, 35 (28%) showed two clones and 9 (7%) had three or more clones. A high degree of correlation (r >/= 0.89; P < 0.001) was found between FISH and flow cytometry as regards the overall quantitative DNA changes detected with both techniques, the former being more sensitive. Among the cases with chromosome abnormalities, the earliest tumor cell clone observed was frequently characterized by the loss of one or more chromosomes (64% of all meningiomas); loss of either a single chromosome 22 or, less frequently, of a sex chromosome (X or Y) and del (1p) was commonly found as the single initial cytogenetic aberration (30%, 5%, and 5% of the cases, respectively). Interestingly, an isolated loss of chromosome 22 was only found as the initial abnormality in one out of 14 atypical/anaplastic meningiomas, while the same cytogenetic pattern was present in the ancestral tumor cell clone of 32% of the benign tumors. Cytogenetic patterns based on chromosome gains were found in the ancestral tumor cell clone in 4% of the patients, 2% corresponding to tetraploid tumors. Overall, cytogenetic evolution of the earliest tumor cell clones was frequently associated with tetraploidization (31%). Our results show that meningiomas are genetically heterogeneous tumors that display different patterns of numerical chromosome changes, with the presence of more than one tumor cell clone detected in almost half of the cases including all atypical/anaplastic cases. Interestingly, the pathways of intr...

Fluorescent In Situ Hybridization 1p/19q Deletion/Imbalance Analysis of Low-Grade and Atypical Meningiomas

“…16) Chromosome 22q deletion and/or mutation of neurofibromatosis type 2 gene (NF2) are most frequently detected as the earliest genetic aberrations and found in meningiomas of all malignancy grades, indicating that inactivation of this gene represents an early event in the pathogenesis of meningiomas. 14,15,19,20) LOH for loci on chromosome 22q and mutations in the NF2 locus probably do not play a role in the development of malignancy in meningiomas. 16) Thus, the assessment of chromosome 22q is not suitable for the alterations associated with progression of meningiomas.…”

“…LOH associated with meningioma progression has been extensively researched, 2,16,18) but only limited data on chromosomal aberrations by FISH are available. 3,6,[13][14][15] FISH analysis should be assessed as numerical genomic abnormalities at the cytogenetic level, not as the rate of chromosome gain or loss. 6,14,15) Assessment of FISH deletion status is useful for the evaluation of chromosomal instability of meningiomas.…”

Intratumoral patterns of clonal evolution in gliomas

“…Only those spots with a similar size, intensity and shape in non-overlapping nuclei, were counted; doublet signals were considered as single spots. Cut-offs used to define the presence of numerical abnormalities for each individual chromosome, were based on the analysis of normal human tissue samples, as previously described in detail [31]. Briefly, gains and losses of specific chromosome regions were considered to occur when ≥5% and ≥10% of the nuclei showed an increased and decreased number of fluorescent signals (spots) with respect to normal diploid cells, respectively.…”

“…Definition of the exact tumor cell clones present in each sample was based on the presence of nuclei carrying identical numbers of hybridization spots for all probes analyzed in that tumor sample. In this study, only those groups of cells showing identical cytogenetic profiles which represented ≥5% of the tumor cells in a sample were considered to be a clone [31]. The ancestral tumor cell clone was identified as that tumor cell clone which carried genetic abnormalities common to all other tumor cell clones.…”

Hyperdiploidy defines a distinct cytogenetic entity of meningiomas

“…The most common primary cytogenetic feature of all grades of meningioma is monosomy 22, whereas tumor progression and recurrence is associated with stronger hypodiploidy, in particular monosomy of chromosomes 14 and/or 18, and loss of the short arm of a chromosome 1 [2][3][4][5][6]. Hyperdiploidy, on the other hand, has long been known to be found in rare instances of meningiomas [2,7,8]. Beyond these anecdotal reports of karyotypes, hyperdiploidy in meningiomas has been demonstrated so far mainly through FISH with probes for single chromosomes, such as # 6, 7, 10, 17, 20, 22, and X [9][10][11].…”