Genomic analysis of the origins and evolution of multicentric diffuse lower-grade gliomas

Abstract

Background: Rare multicentric lower-grade gliomas (LGGs) represent a unique opportunity to study the heterogeneity among distinct tumor foci in a single patient and to infer their origins and parallel patterns of evolution.

Methods: In this study, we integrate clinical features, histology, and immunohistochemistry for 4 patients with multicentric LGG, arising both synchronously and metachronously. For 3 patients we analyze the phylogeny of the lesions using exome sequencing, including one case with a total of 8 samples from the 2 lesions.

Results: One patient was diagnosed with multicentric isocitrate dehydrogenase 1 (IDH1) mutated diffuse astrocytomas harboring distinct IDH1 mutations, R132H and R132C; the latter mutation has been associated with Li-Fraumeni syndrome, which was subsequently confirmed in the patient's germline DNA and shown in additional cases with The Cancer Genome Atlas data. In another patient, phylogenetic analysis of synchronously arising grade II and grade III diffuse astrocytomas demonstrated a single shared mutation, IDH1 R132H, and revealed convergent evolution via non-overlapping mutations in ATRX and TP53. In 2 cases, there was divergent evolution of IDH1-mutated and 1p/19q-codeleted oligodendroglioma and IDH1-mutated and 1p/19q-intact diffuse astrocytoma, occurring synchronously in one case and metachronously in a second.

Conclusions: Each tumor in multicentric LGG cases may arise independently or may diverge very early in their development, presenting as genetically and histologically distinct tumors. Comprehensive sampling of these lesions can therefore significantly alter diagnosis and management. Additionally, somatic IDH1 R132C mutation in either multicentric or solitary LGG identifies unsuspected germline TP53 mutation, validating the limited number of published cases.

Fig. 1

Multifocal tumors exhibit heterogeneity of core mutations required for gliomagenesis. Summary of diverging early mutations and MRI of Patients 1–3.

Fig. 2

Protein expression and phylogenetic analyses among the tumors in Patient 1 revealed mutational heterogeneity in IDH1 and ATRX. (A) This patient had 2 non-enhancing, T2 bright left frontal tumors. The right bottom image shows the resection cavities of the lesions. (B) Phylogenetic tree derived from somatic mutations from exome sequencing. Branch length is proportional to the number of coding single nucleotide somatic mutations. Aberrations identified by IHC are labeled in blue. (C) IHC using IDH1 R132H antibody. Scale bar, 20 μm.

Fig. 3

Protein expression and genetic differences among the image-guided biopsies of the bilateral tumors from Patient 2. (A) H&E and IHC for IDH1 R132H, p53, and ATRX on the left-side tumor. (B) Phylogenetic tree derived from somatic mutations from exome sequencing. Genes frequently mutated in glioma inferred from exome sequencing data are highlighted. (C) H&E and IHC for IDH1 R132H, p53, and ATRX on the right-side tumor (IHC staining from a separate piece to the image-guided biopsies). Scale bar, 20 μm.

Fig. 4

Protein expression and genetic differences of the bilateral tumors of Patient 3. (A) Patient 3 presented with bilateral tumors. The left side has a 1p/19q codeletion and the right side has 1p/19q intact with 19q loss (different breakpoints than the 1p/19q codeletion; Supplementary Figure S4). (B) P53 and ATRX IHC on the left- and right-side tumors. Scale bar, 20 μm. (C) A phylogenetic tree derived from somatic mutations from exome sequencing. Genes frequently mutated in glioma, copy number changes (pink) inferred from exome sequencing, and protein expression (blue) are highlighted.

Fig. 5

Protein expression and genetic characteristic exhibited by the multicentric lesions of Patient 4. (A) H&E and IHC for p53 and ATRX on the first surgery. (B) MRI scan of the lesions of the first and second surgeries of Patient 4. (C) H&E and IHC for p53 and ATRX on the second surgery. Scale bar, 20 μm.