(P 228) WHAT IS THE SIGNIFICANCE OF INDETERMINATE PULMONARY NODULES IN HIGH GRADE SOFT TISSUE SARCOMA? A RETROSPECTIVE COHORT STUDY

Objective: Sarcomas are rare, aggressive cancers which frequently metastasise to the lungs. Following diagnosis, patients typically undergo staging by means of a CT scan of their chest. Whilst the scan often identifies no lung nodules or frank metastases, indeterminate pulmonary nodules (IPNs) are often reported. Delineating between benign and malignant lung nodules is important with regards to treatment decision making, with complete resection of metastatic disease important for survival in sarcoma. Whilst the presence of IPNs has been shown to be associated with decreased overall survival (OS) in osteosarcoma, the significance of IPNs in high grade soft tissue sarcoma (STS) is unclear. This study aims to ascertain the clinical relevance of IPNs in patients with high grade STS, their effect on survival and factors associated with their progression to metastatic disease.

Methods: All patients treated at the North of England Bone and Soft Tissue Tumour Service for high grade STS between 01/01/2010 and 01/05/2020 were identified from a prospectively maintained database. Patient were excluded if they had low grade sarcomas, intracranial, retroperitoneal or visceral locations, of if we had no access to their staging scans. IPNs were classified as non-calcified lung nodules < 10mm in diameter. CT staging scans and reports were reviewed, as well as any subsequent imaging, and survival data collected from patient records. In patients with IPNs at diagnosis developing lung metastases, it was noted whether this was progression of the IPNs or the development of new lesions. Statistical analysis was conducted in SPSS and R studio.

Results: 389 patients were identified as suitable and included in the study. Patients had a median age of 61.9 years old and there was a male predominance of 62.4%. On CT staging scans, 57.1% of patients had no signs of lung metastases, 34.4% of patients had IPNs and 8.5% had frank lung metastases (Figure 1). There was a trend towards increased risk of developing lung metastases and poorer OS in patients with IPNs, although neither reached significance (p=0.14 and p=0.19 respectively) (Figure 2). Of those presenting with IPNs, 20.1% progressed to metastases; they were more likely to progress if IPNs were 5mm or greater in diameter (p=0.006), multiple IPNs (p=0.013) or bilateral IPNs (p=0.022), as well as in patients with primaries 5cm or larger (p=0.014), grade 3 primaries (p=0.009) or primaries arising deep to the fascia (p=0.041) (Table 1). The median time to progression of IPNs was 143 days; 18.5% of IPNs that progressed did so after 12 months however. Patients with undifferentiated pleomorphic sarcoma (n=100) and myxofibrosarcoma (n=100) were analysed independently; IPNs at diagnosis were not associated with an increased likelihood of developing lung metastases or with decreased OS in either subtype.

Conclusion: It is crucial to consider the primary tumour as well the IPNs when considering the risk of progression. Surveillance CT scans should be carried out within 6 months and repeated at 12 months, although improved imaging technologies are necessary to improve differentiation between benign and malignant nodules. The association between IPNs and survival in patients with high grade STS remains unclear and requires further study. Further study is also required to ascertain the influence of histological subtype on the risk of IPN progression.