Retroperitoneal sarcoma

Retroperitoneal sarcomas are a site-defined group: well-differentiated and dedifferentiated liposarcoma make up about two thirds, leiomyosarcoma about a fifth, and solitary fibrous tumour, MPNST and undifferentiated pleomorphic sarcoma most of the rest. They present late as huge painless masses that displace the kidney, colon and pancreas, and the dominant pattern of failure differs by histology: liposarcoma recurs locally in the abdomen, often repeatedly and years later, while leiomyosarcoma metastasises to the liver and lungs. The Transatlantic Australasian Retroperitoneal Sarcoma Working Group consensus documents define the modern approach.

Complete en bloc resection at first presentation, removing adjacent organs such as kidney, colon and psoas to secure a margin, is the only curative treatment and has been associated with better local control in reference centres since the reports of Gronchi and Bonvalot in 2009. Adjuvant therapies were tested in the EORTC STRASS trial, which randomised 266 patients to preoperative radiotherapy plus surgery or surgery alone and found no improvement in abdominal recurrence-free survival overall, though an unplanned analysis suggested benefit in well-differentiated and low-grade dedifferentiated liposarcoma. Preoperative radiotherapy is therefore not routine and is discussed case by case for liposarcoma.

Systemic therapy is histology-driven: doxorubicin with ifosfamide for dedifferentiated liposarcoma, doxorubicin with dacarbazine or trabectedin for leiomyosarcoma (LMS-04), and eribulin and MDM2 inhibitors for liposarcoma. The STRASS2 trial is testing neoadjuvant chemotherapy against surgery alone in high-risk dedifferentiated liposarcoma and leiomyosarcoma, and repeat surgery for recurrence, selected by growth rate and multifocality, remains the main tool after relapse.