Mutation analysis of the EGFR gene and its downstream signaling pathway in thymic carcinoma patients from a Chinese Han population

Depiction of the Genetic Alterations and Molecular Landscapes of Thymic Epithelial Tumors: A Systematic Review and Meta-Analysis

Thymic epithelial tumors (TETs), consisting of thymomas, thymic carcinomas (TCs), and thymic neuroendocrine tumors, are rare diseases. Surgery remains the prime option in resectable and early-stage TETs, while chemotherapy, targeted therapy, and immunotherapy are also potential treatment modalities. However, the inadequate comprehension of the molecular landscape of TETs impedes the exploitation of such therapies. Hence, we conducted a meta-analysis which includes 21 studies reporting on genomic alterations in TETs and 14 studies reporting on PD-L1 expression levels, respectively. The pooled estimated rates of the most frequently mutated genes and PD-L1 expression levels were analyzed using the R software. We uncovered that the pooled estimated overall mutation rate is 0.65 ([0.49; 0.81]), and the top three genes with highest mutation frequency in thymomas and TCs are GTF2I (0.4263 [0.3590; 0.4936]), TP53 (0.1101 [0.0000; 0.2586]), and RAS (0.0341 [0.0104; 0.0710]), and TP53 (0.1797 [0.0732; 0.3203]), CDKN2A (0.0608 [0.0139; 0.1378]), and TET2 (0.0318 [0.0087; 0.0639]), respectively. A uniform GTF2I mutational rate in thymomas and TP53 mutational rate in thymic squamous cell carcinomas (TSCCs) are also observed. The pooled estimated expression level of PD-L1 is 0.71 ([0.59-0.81]). This systematic review provides an overview of the gene alteration landscape and PD-L1 expression levels in TETs, discovers several potential confounding factors that may contribute to the high heterogeneity, and facilitates deeper investigations into the elucidation of the molecular landscape of TETs.

Complete remission following icotinib administration in an advanced ectopic thymic carcinoma patient harbouring the EGFR exon 19 deletion

Background

Ectopic thymic carcinoma (TC) is an extremely rare disease with a poor prognosis. The main treatment for early TC is surgery, although an effective treatment for advanced TC is lacking.

Methods

We present the case of a 61‐year‐old man with advanced posterior mediastinum thymic squamous cell carcinoma. Amplification refractory mutation system (ARMS)–polymerase chain reaction (PCR) analysis was used to investigate the molecular and mutational characteristics of this tumour.

Results

After chemotherapy and radiotherapy, the tumour showed disease progression. Immunohistochemistry revealed that the tumour was positive for CD117 (specific for primary TC), CK19, CD56 and Ki67. ARMS‐PCR analysis revealed an EGFR exon 19 deletion in the patient. The patient subsequently received icotinib treatment and achieved complete remission for 3 years.

Conclusions

This case report suggests that tyrosine kinase inhibitors are a potential treatment strategy for patients with TC harbouring EGFR alterations.

Next-generation sequencing in thymic epithelial tumors uncovered novel genomic aberration sites and strong correlation between TMB and MSH6 single nucleotide variations

Thymic epithelial tumors (TET) including thymomas and thymic carcinomas are rare, but they are common primary tumors in the anterior mediastinum. The etiology and tumorigenesis of TET remain unclear. To better understand the novel aberrations of this rare tumor and provide more significant mutation sites for targeted therapy, we performed next-generation sequencing detection on 55 patients with TET. Our results showed that most genes in 12 core pathways harbored aberrations of indeterminate potential. In 4 genes (ARID1A, KMT2C, TGFBR2 and MAP3K1), the indel frequency was above 90%. Dozens of genes, including TGFBR2, KMT2C, PRKDC, ATR, CHD2, SDHA, KDM5A, CHEK1, MSH6 and POLE, possessed frameshift indel with different frequencies in different hotspot sites, which could be the new targets of therapy for TET. For the first time, we revealed a strong correlation between the tumor mutational burden and single nucleotide variations, but not frameshift, on DNA mismatch repair gene MSH6 in TET.

A mutation analysis of the EGFR pathway genes, RAS, EGFR, PIK3CA, AKT1 and BRAF, and TP53 gene in thymic carcinoma and thymoma type A/B3

AIMS

Thymic carcinoma is rare and usually has a fatal outcome. Gene mutations in the epidermal growth factor receptor (EGFR) signalling pathway and TP53 have not been well analysed in thymic carcinoma.

METHODS AND RESULTS

We examined a large cohort of thymic carcinoma and thymoma type A/B3 and looked for gene mutations in the RAS family, EGFR, PIK3CA, AKT1, BRAF and TP53. Among 54 thymic carcinoma cases, RAS family mutations were detected in 10 cases, EGFR in two, PIK3CA in one, AKT1 in one, BRAF in none and TP53 in five. Among 33 thymoma type A/B3 cases, HRAS gene mutation were found in one, PIK3CA in two and AKT1 in one. All these mutations were those of missense type activating mutations. RAS family mutations were significantly more frequent in thymic carcinoma than in thymoma type A/B3 (P = 0.0461). A prognostic analysis focusing on thymic squamous cell carcinoma cases (n = 44) showed that the overall survival was significantly shorter in patients with EGFR pathway mutations (n = 9) than in those without in a univariate analysis (P = 0.0173). Subsequently, EGFR pathway mutations were selected as an independent factor for a poor overall survival in a multivariate analysis (P = 0.0389).

CONCLUSIONS

Mutations in the EGFR pathway and TP53 in thymic carcinoma may be frequent, and the EGFR pathway mutations may be associated with a poor prognosis in thymic squamous cell carcinoma patients. The therapeutic significance of gene mutations in thymic carcinoma should be further clarified.