(P 390) VARIATIONS IN GLOBAL PATTERNS OF CARE FOR RETROPERITONEAL SARCOMAS - A STUDY BY TARPSWG

Objective: Retroperitoneal sarcomas (RPS) are a heterogenous groups of tumours that frequently are large and have complex anatomical relationships. Given a paucity of high-quality data to inform practice, coupled with a wide variety in caseload volume, variations in treatment approach remain apparent. The aim of this study was to examine the variations in patterns of care for RPS between sarcoma referral centres globally, including diagnostic work-up, surgical strategies and the use of neo/adjuvant therapies.

Methods: A retrospective analysis was performed on patients extracted from a multi-institutional prospective observational study (RESAR - NCT03838718) for primary RPS, comprising 19 Transatlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG) referral centres worldwide, between Feb 2017 – July 2022. Patients undergoing curative-intent treatment for RPS with one of the six most common histologic subtypes of RPS were included (dedifferentiated liposarcoma (DDLPS), well-differentiated liposarcoma (WDLPS), leiomyosarcoma (LMS), solitary fibrous tumour (SFT), undifferentiated pleomorphic sarcoma (UPS) and malignant peripheral nerve sheath tumour (MPNST)).
Patients were grouped by institution to calculate the frequency of: pre-treatment biopsy, extent of surgery (number of organs resected; frequency of ipsilateral kidney and colon resection – as a surrogate for multivisceral resection), completeness of surgery and neo/adjuvant treatments. Institutions were categorised according to pre-defined criteria as either high volume (HVC, >13 cases/year) or low volume (LVC, < 13 cases/year). Descriptive statistical analysis was performed for the treatment variables for each of the RPS subtypes.

Results: A total of 1718 patients from 19 sarcoma referral centres were included. 8 centres were categorised as HVC (contributing between 97-353 cases) and 11 as LVC (contributing 5-65 cases). The most common histotypes were DDLPS (49%), LMS (21%) and WDLPS (20%). Preoperative biopsy occurred in 89% of cases and rates of biopsy by centre ranged from 56-100%. Of these, 59% were performed under CT guidance, ranging from 2-96% by centre. Of the 184 patients who were not biopsied prior to treatment, 159 (86%) had either WDLPS or DDLPS.

Overall, 134 patients (8%) received chemotherapy (CT) and 275 patients (16%) received radiotherapy (RT), with 86% of the CT and 93% of the RT patients treated pre-operatively (Figure 1). The histotypes with the highest rates of CT were LMS and MPNST (14-15%) with other subtypes receiving CT in 0-9% of cases. The histotypes with highest rates of RT were UPS and MPNST (36-37% of cases), with other subtypes receiving RT in 10-17% of cases.

There was substantial variability in rates of RT and CT in different subtypes across institutions (Figures 2-3). For DDLPS, RT was never used in 8 centres while 7 centres used RT in 17-53% of cases. In WDLPS, 11 centres never used RT while 5 centres used it in 19-60% of cases. CT was used consistently infrequently in DDLPS, with 15/19 sites using it in 0-4% of cases; yet in LMS there was wide variation, with sites spread evenly between 0-67% of cases.

In terms of surgery (Figure 4), all liposarcomas (WD and DD) and UPS were treated with the most extensive surgery, with a median of 4-5 organs resected, whereas LMS, SFT and MPNST had median 1-2 organs resected. A multivisceral surgical approach was seen in 78% of DDLPS but varied widely, even between HVC (38-85%); and in 66% of WDLPS, varying from 33-87% between HVC.
In patients with liposarcoma, HVC used RT in 18% of DDLPS and 19% of WDLPS cases compared with 7% and 5% respectively in LVC. R2 margins were higher in LVC compared with HVC (16% vs 4%).

Conclusion: Substantial variability in patterns of care exist between referral centres for RPS.
This study helps to define the aspects of care in which most variability exists and helps to refine future research questions.