DICER1-associated central nervous system sarcoma: A comprehensive clinical and genomic characterization of case series of young adult patients

Background

DICER1 alterations are associated with intracranial tumors in the pediatric population, including pineoblastoma, pituitary blastoma, and the recently described "primary DICER1-associated CNS sarcoma" (DCS). DCS is an extremely aggressive tumor with a distinct methylation signature and a high frequency of co-occurring mutations. However, little is known about its treatment approach and the genomic changes occurring after exposure to chemoradiotherapy.

Methods

We collected clinical, histological, and molecular data from eight young adults with DCS. Genomic analysis was performed by Next-generation Sequencing (NGS). Subsequently, an additional germline variants analysis was completed. In addition, an NGS analysis on post-progression tumor tissue or liquid biopsy was performed when available. Multiple clinicopathological characteristics, treatment variables, and survival outcomes were assessed.

Results

Median age was 20 years. Most lesions were supratentorial. Histology was classified as fusiform cell sarcomas (50%), undifferentiated (unclassified) sarcoma (37.5%), and chondrosarcoma (12.5%). Germline pathogenic DICER1 variants were present in two patients, 75% of cases had more than one somatic alteration in DICER1, and the most frequent commutation was TP53. Seven patients were treated with surgery, Ifosfamide, Cisplatin, and Etoposide (ICE) chemotherapy and radiotherapy. The objective response was 75%, and the median time to progression (TTP) was 14.5 months. At progression, the most common mutations were in KRAS and NF1. Overall survival was 30.8 months.

Conclusions

DCS is an aggressive tumor with limited therapeutic options that requires a comprehensive diagnostic approach, including molecular characterization. Most cases had mutations in TP53, NF1, and PTEN, and most alterations at progression were related to MAPK, RAS and PI3K signaling pathways.

Genomic Landscape of Primary Resistance to Osimertinib Among Hispanic Patients with EGFR-Mutant Non-Small Cell Lung Cancer (NSCLC): Results of an Observational Longitudinal Cohort Study

BACKGROUND

Epidermal growth factor receptor (EGFR) mutations (EGFRm) represent one of the most common genomic alterations identified among patients with non-small cell lung cancer (NSCLC). Several targeted agents for patients with EGFRm have been proven safe and effective, including the third-generation tyrosine kinase inhibitor (TKI) osimertinib. Nonetheless, some patients will present with or develop EGFR-TKI resistance mechanisms.

OBJECTIVE

We characterized the genomic landscape of primary resistance to osimertinib among Hispanic patients with EGFR-mutant NSCLC.

METHODS

An observational longitudinal cohort study was conducted with two groups of patients, those with intrinsic resistance (cohort A) and those with long-term survival (cohort B). All patients were treated and followed between January 2018 and May 2022. All patients were assessed for Programmed Cell Death Ligand 1 (PD-L1) expression and Bcl-2-like protein 11 (BIM)/AXL mRNA expression before starting TKI. After 8 weeks of treatment, a liquid biopsy was performed to determine the presence of circulating free DNA (cfDNA), and next-generation sequencing (NGS) was used to identify mutations at the time of progression. In both cohorts, overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) were evaluated.

RESULTS

We found a homogeneous distribution of EGFR-sensitizing mutations in both cohorts. For cohort A, exon 21 mutations were more common than exon 19 deletions (ex19dels) for cohort B (P = 0.0001). The reported ORR for osimertinib was 6.3% and 100% for cohorts A and B, respectively (P = 0.0001). PFS was significantly higher in cohort B (27.4 months vs. 3.1 months; P = 0.0001) and ex19del patients versus L858R (24.5 months, 95% confidence interval [CI] 18.2-NR), vs. 7.6 months, 95% CI 4.8-21.1; P = 0.001). OS was considerably lower for cohort A (20.1 months vs. 36.0 months; P = 0.0001) and was better for patients with ex19del, no brain metastasis, and low tumor mutation burden. At the time of progression, more mutations were found in cohort A, identifying off-target alterations more frequently, including TP53, RAS, and RB1.

CONCLUSION

EGFR-independent alterations are common among patients with primary resistance to osimertinib and significantly impact PFS and OS. Our results suggest that among Hispanic patients, other variables associated with intrinsic resistance include the number of commutations, high levels AXL mRNA, and low levels of BIM mRNA, T790M de novo, EGFR p.L858R presence, and a high tumoral mutational burden.