Evaluation of Heterogeneity in the Coding Region of BRAF, MAP2K1, and MAP2K2 Genes in Primary and Metastatic Melanomas

INTRODUCTION

The incidence of melanoma has been increasing in recent decades. BRAF mutations appear in 50%-70% of melanomas. The BRAF-targeted therapy increased the disease-free survival of patients with metastatic melanoma, but this response may be short, due to several resistance mechanisms, such as the presence of other subclones with mutations. Evaluation of mutations and heterogeneity in the coding region of the BRAF, MAP2K1, and MAP2K2 genes in primary and metastatic melanomas.

PATIENTS AND METHODS

Twenty-seven samples of primary and metastatic superficial spreading melanoma (SSM) and acral lentiginous melanoma (ALM) were analyzed for BRAF, MAP2K1, and MAP2K2 mutations using the next-generation sequencing technique.

RESULTS

In ALM, the mutation rate found was 50% in the BRAF and MAP2K1 genes and 28.6% in MAP2K2. In the SSM, BRAF was mutated in 76.9%, MAP2K1 in 30.8%, and MAP2K2 in 23.2% of the cases. All samples were formed by distinct tumor subclones in the same lesion. Intertumoral heterogeneity was present between primary and metastatic lesions of ALM in BRAF, MAP2K1, and MAP2K2; the cases of SSM were heterogeneous for BRAF and MAP2K1.

CONCLUSION

We sought to evaluate the mutations in the BRAF, MAP2K1, and MAP2K2 genes, revealing a heterogeneous mutation profile in samples of ALM and SSM.

Clinical characteristics of 10 Chinese patients with melorheostosis and identification of a somatic MAP2K1 variant in one case

Background

Melorheostosis (MEL) is an exceptionally rare sclerosing bone dysplasia with asymmetrically exuberant bone formation and soft tissue lesions in a segmental distribution. We aimed to summarize the clinical characteristics of Chinese MEL patients and identify their pathogenic cause.

Methods

In total, 10 Chinese MEL patients were recruited, and clinical manifestations and radiological characteristics were recorded. Sanger sequencing of the LEMD3 gene was performed on peripheral blood samples of all patients, while the exome sequencing of matched peripheral blood, melorheostotic bone, and skin lesion samples was conducted on one patient who provided affected bone and skin tissues. Micro‐computed tomography (micro‐CT) was also used to scan the melorheostotic bone tissue.

Results

We found the average age of the 10 MEL patients was 29.5 years (range 11–40 years), and the major symptoms were bone pain, restricted movement, and bone deformity. The lesions sites were mainly located in femur (8/10), tibia (8/10), fibula (6/10), and foot (7/10), the next was pelvis (4/10), and the last were patella (1/10), hand (1/10) and spine (1/10). Radiological examinations showed a mixture of hyperostosis consisting of classic “dripping candle wax,” “osteoma‐like,” or “myositis ossificans‐like” patterns in most patients. No germline pathogenic variants in the LEMD3 gene were found in all patients, but a disease‐causing somatic variant of MAP2K1 (c.167A > C, p.Gln56Pro) was detected in melorheostotic bone from one patient. Moreover, the micro‐CT analysis showed increased porosity in the melorheostotic bone with somatic MAP2K1 variant.

Conclusion

This is a summary of the clinical characteristics of Chinese MEL patients and we first identify the somatic MAP2K1 variant in Chinese patients. Our findings validate the molecular genetic mechanism of MEL and broaden its phenotype spectrum in the Chinese population.

Role of Targeted Sequencing in Routine Diagnostics of Spitz Melanocytic Neoplasms-An Analysis of 70 Cases

BACKGROUND

There is growing evidence that the Spitz group of melanocytic neoplasms should be restricted to those harboring kinase receptor fusions and HRAS mutations/11p15 amplification. The presence of genomic alterations characteristic of conventional melanomas (BRAF and NRAS mutations) precludes a diagnosis of a Spitz neoplasm. It is often challenging to distinguish Spitz neoplasms from conventional melanomas with spitzoid morphology on histopathological grounds alone.

METHODS

We report a series of 70 consecutive melanocytic tumors in which targeted sequencing was indicated to distinguish Spitz from spitzoid neoplasms and to classify Spitz neoplasms along the biological spectrum.

RESULTS

Final diagnoses incorporating molecular results included 12 conventional melanomas (nine of which with NRAS mutations), five Spitz melanomas, 35 atypical Spitz tumors, eight Spitz nevi, three melanocytic tumors with a MAP2K1 mutation, and seven desmoplastic Spitz nevi/tumors. There were significant discrepancies between initial diagnoses and final diagnoses after incorporating molecular results in 24 (34%) cases, including nine conventional melanomas favored to be Spitz neoplasms and nine Spitz neoplasms favored to be conventional melanomas.

CONCLUSIONS

It is often not possible to reliably distinguish Spitz neoplasms from spitzoid melanocytic tumors without identifying their driver genomic alterations. Applying next-generation sequencing in diagnostically problematic tumors improves diagnostic accuracy.