Comprehensive Molecular and Clinicopathological Profiling of Lymphatic Malformations.

PURPOSE: Lymphatic malformations (LMs) are rare, slow-flow vascular malformations often driven by somatic PIK3CA mutations. However, the role of PIK3CA mutations in the pathogenesis of LMs is not yet fully understood. In this study, we conducted an integrated analysis of LMs to clarify how PIK3CA mutations relate to clinical presentation, histopathological features, and molecular characteristics.

MATERIALS AND

METHODS

We retrospectively analyzed 34 LM cases. PIK3CA mutations were assessed using targeted next-generation sequencing with a custom gene panel. We also evaluated clinical and histopathological findings and performed immunohistochemistry. Spatial transcriptomics was performed on two PIK3CA-mutant LM cases.

RESULTS

Somatic PIK3CA mutations were identified in 20/34 patients (58.8%). Clinical variables (age, sex, and lesion location) and most histopathological parameters were comparable between mutant and non-mutant LMs, although mutant LMs more often exhibited a scattered growth pattern of malformed vessels. The malformed vessel microenvironment, including fibrous stroma, lymphoid aggregates, and macrophages, was commonly observed regardless of the mutational status. Immunohistochemistry showed higher PI3K/AKT/mTOR pathway activation in the lymphatic endothelial cells (LECs) in LMs than in normal lymphatic vessels, independent of PIK3CA status, although this pathway is commonly activated by gain-of-function PIK3CA mutations. Phosphorylated AKT levels in LMs significantly increased with age. Spatial transcriptomics identified upregulation of 10 genes in LEC-containing regions of PIK3CA-mutant LMs. Among the upregulated genes, NFATC1, which regulates embryonic lymphangiogenesis, was highly expressed in LM LECs, suggesting that the calcineurin-NFAT pathway may contribute to LM pathogenesis.

CONCLUSIONS

Overall, LMs share key pathogenic features irrespective of mutational status. This detailed analysis, focusing on LECs and the microenvironment, may offer insights into the mechanisms underlying LM pathogenesis and its implications for targeted therapies.