RESUMO
In the Drug Rediscovery Protocol (DRUP), patients with cancer are treated based on their tumor molecular profile with approved targeted and immunotherapies outside the labeled indication. Importantly, patients undergo a tumor biopsy for whole-genome sequencing (WGS) which allows for a WGS-based evaluation of routine diagnostics. Notably, we observed that not all biopsies of patients with dMMR/MSI-positive tumors as determined by routine diagnostics were classified as microsatellite-unstable by subsequent WGS. Therefore, we aimed to evaluate the discordance rate between routine dMMR/MSI diagnostics and WGS and to further characterize discordant cases. We assessed patients enrolled in DRUP with dMMR/MSI-positive tumors identified by routine diagnostics, who were treated with immune checkpoint blockade (ICB) and for whom WGS data were available. Patient and tumor characteristics, study treatment outcomes, and material from routine care were retrieved from the patient medical records and via Palga (the Dutch Pathology Registry), and were compared with WGS results. Initially, discordance between routine dMMR/MSI diagnostics and WGS was observed in 13 patients (13/121; 11%). The majority of these patients did not benefit from ICB (11/13; 85%). After further characterization, we found that in six patients (5%) discordance was caused by dMMR tumors that did not harbor an MSI molecular phenotype by WGS. In six patients (5%), discordance was false due to the presence of multiple primary tumors (n = 3, 2%) and misdiagnosis of dMMR status by immunohistochemistry (n = 3, 2%). In one patient (1%), the exact underlying cause of discordance could not be identified. Thus, in this group of patients limited to those initially diagnosed with dMMR/MSI tumors by current routine diagnostics, the true assay-based discordance rate between routine dMMR/MSI-positive diagnostics and WGS was 5%. To prevent inappropriate ICB treatment, clinicians and pathologists should be aware of the risk of multiple primary tumors and the limitations of different tests. © 2024 The Pathological Society of Great Britain and Ireland.
Assuntos
Reparo de Erro de Pareamento de DNA , Inibidores de Checkpoint Imunológico , Instabilidade de Microssatélites , Humanos , Feminino , Masculino , Pessoa de Meia-Idade , Idoso , Inibidores de Checkpoint Imunológico/uso terapêutico , Imunoterapia/métodos , Sequenciamento Completo do Genoma , Adulto , Biomarcadores Tumorais/genética , Neoplasias/genética , Neoplasias/terapia , Neoplasias/patologia , Idoso de 80 Anos ou mais , Neoplasias Colorretais/genética , Neoplasias Colorretais/patologia , Neoplasias Colorretais/terapiaRESUMO
High-throughput sequencing efforts in molecular tumour diagnostics detect increasing numbers of novel variants, including variants predicted to affect splicing. In silico prediction tools can reliably predict the effect of variant disrupting canonical splice sites; however, experimental validation is required to confirm aberrant splicing. Here, we present RNA analysis performed for 13 canonical splice site variants predicted or known to result in splicing in the cancer predisposition genes MLH1, MSH2, MSH6, APC and BRCA1. Total nucleic acid was successfully isolated for 10 variants from eight formalin-fixed paraffin-embedded (FFPE) tumour tissues and two B-cell lines. Aberrant splicing was confirmed in all six variants known to result in splicing. Of one known variant in the B-cell line, aberrant splicing could only be detected after formalin fixation, which indicated that formalin fixation could possibly inhibit RNA degradation. Aberrant splicing was concluded in three of four predicted splice variants of uncertain significance, supporting their pathogenic effect. With this assay, somatic splice variants can be easily and rapidly analysed, enabling retrospective analysis to support the pathogenicity of variants predicted to result in splicing when only FFPE material is available.
Assuntos
Neoplasias da Mama/genética , Testes Genéticos/métodos , Mutação , Splicing de RNA , Análise de Sequência de RNA/métodos , Proteína da Polipose Adenomatosa do Colo/genética , Proteína BRCA1/genética , Neoplasias da Mama/patologia , Proteínas de Ligação a DNA/genética , Feminino , Testes Genéticos/normas , Humanos , Proteína 1 Homóloga a MutL/genética , Proteína 2 Homóloga a MutS/genética , Análise de Sequência de RNA/normas , Inclusão do Tecido/métodos , Inclusão do Tecido/normas , Fixação de Tecidos/métodos , Fixação de Tecidos/normasRESUMO
Many suspected Lynch Syndrome (sLS) patients who lack mismatch repair (MMR) germline gene variants and MLH1 or MSH2 hypermethylation are currently explained by somatic MMR gene variants or, occasionally, by germline POLE variants. To further investigate unexplained sLS patients, we analyzed leukocyte and tumor DNA of 62 sLS patients using gene panel sequencing including the POLE, POLD1 and MMR genes. Forty tumors showed either one, two or more somatic MMR variants predicted to affect function. Nine sLS tumors showed a likely ultramutated phenotype and were found to carry germline (n=2) or somatic variants (n=7) in the POLE/POLD1 exonuclease domain (EDM). Six of these POLE/POLD1-EDM mutated tumors also carried somatic MMR variants. Our findings suggest that faulty proofreading may result in loss of MMR and thereby in microsatellite instability.
