Objective:

To investigate the pathological morphology, immunophenotype, and molecular genetic characteristics of recurrent low-grade endometrial stromal sarcoma (LG-ESS) through the analysis of paired primary and recurrent tumor samples, highlighting the clinical significance of these findings.

Key Findings:

• All cases showed consistent JAZF1 or PHF1 gene rearrangements in both primary and recurrent tumors, indicating molecular stability.
• Immunophenotypic alterations were observed during recurrence, including loss of PR expression and loss of CD10 expression in different cases, which may impact treatment strategies.
• The median follow-up time was 84 months, with recurrence intervals ranging from 3 to 12 years, and all patients remained alive following treatment.

Interpretation:

Core driver gene rearrangements remain stable during recurrence in LG-ESS, while immunophenotypic evolution may occur, suggesting the need for re-evaluation of biomarkers at recurrence to guide treatment.

Limitations:

• The study is based on a small sample size of four patients, which may limit the generalizability of the findings.
• Longitudinal studies on recurrence mechanisms in LG-ESS are limited, and potential biases in retrospective studies should be considered.

Conclusion:

Long-term follow-up is essential due to the characteristic tendency for late recurrence in LG-ESS, emphasizing the need for ongoing monitoring and potential re-evaluation of treatment strategies.