(P 218) PRIMARY PELVIC SOFT TISSUE SARCOMAS (PELVISARC): OUTCOMES IN A SERIES OF 401 PATIENTS FROM THE TRANSATLANTIC AUSTRALASIAN RETROPERITONEAL SARCOMA WORKING GROUP (TARPSWG)

Objective: Pelvic soft tissue sarcomas (PSTS) have been grouped with retroperitoneal sarcomas (RPS) in major surgical series to date. Most recent TARPSWG data showed a 5-year local recurrence-free survival (LRFS) of 74.1%, distant metastasis-free survival (DMFS) of 79% and overall survival (OS) of 67% in a RPS-PSTS grouped series. Recent expert guidelines outlined recommendations for RPS may not apply to PSTS. We aimed to describe patterns of presentation, treatment modalities and outcome of PSTS treated at TARPSWG centers to offer a more comprehensive picture of these tumors.

Methods: A retrospective analysis of adult, primary, localized PSTS treated between 2005 and 2018 at 23 TARPSWG centers was performed. Definition of PSTS was tumors originating from non-visceral pelvic structures. Tumor extension into the abdominal cavity and herniation through the sciatic notch, the obturator foramen and/or inguinal ligament were included. Gastrointestinal stromal tumors (GISTs), gynecological, urogenital, Ewing family sarcomas and desmoids were excluded. Patients’ clinical, histological and treatment characteristics were collected, and LRFS, DMFS, OS and disease-specific survival (DSS) were calculated through September 2021. Survival analysis was performed using the Kaplan-Meier method and log rank test. Uni- and multivariate regression analysis was performed to identify prognostic factors.

Results: Of 448 identified patients, 401 (89.5%) underwent surgery. Median age was 57 years (IQR 46-67), 252 (62.8%) were men and 357 (89%) had an ECOG < 2. Median tumor size was 13 cm (IQR 8-18); histologic type distribution is shown in Fig 1, with leiomyosarcoma (LMS) being the most frequent histologic subtype (24%), followed by solitary fibrous tumor (SFT) (18%). Tumor grade frequency was as follows: 123 (30.7%) Grade 1, 140 (34.9%) Grade 2 and 120 (29.9%) Grade 3 tumors. Complete resection (R0/R1) was obtained in 90.8% cases. Adjacent organ resection pattern is shown in Fig 2a; median number of resected organs was 2 (IQR 1-3), with 115 patients (28.7%) requiring ≥ 4. Mean hospital stay was 9 days (IQR 7-15) and severe complications (Clavien-Dindo grade ≥3) occurred in 78 patients (19.5%), with 41 (10.2%) requiring reoperation and a 30-day mortality of 2.7%. Multimodal treatment modality and frequency significantly differed across histologies as shown in Fig 2b, with 104 patients (25.9%) receiving chemotherapy, 162 (40.4%) radiotherapy and 68 (16.9%) receiving both. With a median follow-up of 53 months (IQR 30-87), 5-year LFRS was 62.7% (SE ±2.8), 5-year DMFS was 66.1% (SE ±2.7), 5-year OS was 69.6% (SE ±2.6), and 5-year DSS was 72.3% (SE ±2.6). Rates of LR, DM and DSS were significantly different when histological subtypes were compared (p< 0.001) (Fig 3). Multivariate regression analysis (Table 1) showed significantly higher mortality risk for Grade 3 tumors (HR 7.6, p < 0.001). DDLPS was the histology at highest risk of LR (HR 4.09, p=0.004), and LMS at highest risk of DM (HR 2.34, p=0.04).

Conclusion: Retrospective analysis of PSTS exhibited specificities in terms of surgical anatomy, histology distribution and prognosis, somewhat different from previous RPS literature. Major vascular and nerve resection are often required, claiming for treatment by high volume, multidisciplinary teams. Although observed OS for PSTS is similar to previous series grouped with RPS, LRFS and DMFS are lower when PSTS are analysed separately. Notably, no sarcoma-related deaths were recorded among pelvic WDLPS. Neoadjuvant and/or adjuvant treatment was commonly offered. These results suggest that the natural history and surgical management of PSTS should be considered distinct to RPS.

Figure 1.docx

Figure 2.docx

Figure 3.docx

Table 1.docx