(P 428) OLIGOMETASTASES IN EXTREMITY SOFT TISSUE SARCOMA : SUBTYPE-SPECIFIC ANALYSES OF CHARACTERISTICS AND OUTCOMES

Objective: Oligometastases is considered as an intermediate between localized and widespread metastatic disease and is increasingly recognized as an opportunity to control the disease in the long term by giving appropriate local treatment. Soft tissue sarcoma (STS) metastases is often limited to a single organ, the lung, at the time of initial metastases. Although guidelines for the management of oligometastatic disease for common malignancies are already in place, the rarity and the heterogeneity of extremity STS make it difficult to set up guidelines of high level of evidence. This study aimed to examine clinical characteristics and outcomes of oligometastatic STS in addition to its subtype-specific traits.

Methods: This retrospective, single center study examined patients diagnosed with oligometastatic STS from January 2000 to April 2023 at a sarcoma center in South Korea. Inclusion criteria were pathologic diagnosis of sof tissue sarcoma with oligometastasis, defined as less than 5 metastatic lesions in 3 or less organs. Clinical features, oncologic outcomes, prognostic factors, and subtype-specific traits were analyzed.

Results: A total of 170 patients with median follow up of 52.5 months were reviewed (Table 1). Surgery was the most common choice of local ablative therapy (81.2%), followed by radiotherapy (14.4%), and radiofrequency ablation (1.7%).
Of the 170 STS with oligometastasis, 93 (54.7%) died of the disease, 34 (20%) were alive with disease, and 43 (25.3%) had no evidence of the disease at the last follow up. Five-year progression free survival (PFS) and disease specific survival (DSS) since oligometastases diagnosis were 28.1% (Fig. A) and 42.6% (Fig. B), respectively. For PFS after LAT of the oligometastases, prognostic factors were primary tumor size (p< 0.025), primary tumor grade (p< 0.048), metastases-free interval (MFI, p< 0.000), and primary site tumor control (p< 0.003) in univariate analysis. Multivariate analysis showed that MFI (p< 0.002) is an independent risk factor for PFS. For DSS after the diagnosis of oligometastases, prognostic factors were primary tumor size (p< 0.022), oligometastatic lesion size (p< 0.005), MFI (< 0.006), and primary site tumor control (p< 0.000). Multivariate analysis revealed oligometastatic lesion size (p< 0.041), MFI (p< 0.011), and primary site tumor control (p< 0.012) as independent risk factors for DSS.
STS subtypes demonstrated varying metastatic patterns (Table 2). Of the 1243 STS patients who received surgery 358 patients (28.8%) had metastases. Of the 358 patients, 170 (47.5%) were oligometastatic and 188 (52.5%) were polymetastatic. MLS had notably high portion (75%) of oligometastases. Median PFS for UPS (7 months), MFS (7.5 months) was shorter than that of the overall STS (10 months). Median PFS for SS (16 months) and LMS (18 months) were relatively longer. Median DSS for UPS (23 months), MFS (24 months), MPNST (19months) were shorter than that of the overall STS with oligometastases (29 months). On the other hand, median DSS for MLPS (38 months), SS (31 months), and LMS (38 months) were relatively longer.

Conclusion: Oligometastases is relatively common in extremity STS. Longer MFI, smaller size of metastasis and primary site tumor control are associated with better outcome. The patterns and outcomes of oligometastases seem to differ by the histological subtype. These results may provide insights on subtype-specific management of oligometastasis in extremity STS.