Differential diagnosis in challenging spindle cell neoplasm of the retroperitoneum – debate around a case of mast-cell rich deep leiomyoma

Retroperitoneal spindle cell neoplasms represent a rare and heterogeneous group of tumors that are often diag­nos­ti­cally challenging. These tumors include a wide spectrum of benign, intermediate and malignant en­ti­ties, many of which require detailed histopathologic and im­mu­no­his­to­che­mi­cal evaluation for accurate clas­si­fi­ca­tion. We report an interesting case referred to our service for con­sul­ta­tion and immunohistochemical evaluation, in which the original diagnosis was revised after thorough his­to­patho­lo­gi­cal review and an extended panel of im­mu­no­his­to­che­mi­cal studies revealed a different entity within this broad spectrum. This case highlights the importance of considering the full range of retroperitoneal spindle cell neo­plasms and of employing comprehensive morphologic and immunophenotypic assessment to achieve the most ac­cu­rate diagnosis, which is essential for appropriate prog­nos­tic stratification and therapeutic management. In ad­di­tion, it illustrates the potential pitfalls of a narrowly fo­cused diagnostic evaluation which may underscore the importance of comprehensive clinical, macroscopic, mi­cro­sco­pic, immunophenotypic and sometimes molecular cor­re­la­tions in challenging cases.