Evaluation of tumor immune microenvironment for PD-L1 score and tumor infiltrating lymphocytes in high grade osteosarcomas and their correlation with disease progression.

Abstract

e23510 Background: Tumor Immune Micro-environment is being increasingly recognised as a potential target for improving overall survival for osteosarcomas, especially in the metastatic setting. Our study purpose was to evaluate the PD- L1 (Programmed cell Death- Ligand 1) expression in neoplastic cells well as Tumor Infiltrating Lymphocyte (TIL) density of osteosarcoma specimens and correlate it with oncological outcomes. Materials & Methods: A prospective cohort study was conducted between March 2017 and March 2022 among osteosarcoma patients who underwent primary biopsy and neo-adjuvant chemotherapy followed by surgical excision at our centre. We excluded patients who had alternative diagnoses such as low grade osteosarcoma, secondary osteosarcoma, recurrent osteosarcoma as well as patients who had undergone initial treatment (chemotherapy/ surgery) outside our institute. De-paraffinized sections (4μ) incubated with primary antibody (PDL1) and a universal secondary detection kit used. Average percentage of positive cells calculated from at least 10 representative fields at 400X magnification. Positive staining was considered when ≥1% cells showed positivity. IHC scoring of PD-L1 was graded as negative, low positive and high positive. We calculated the number of TILs under 400X magnification in ten fields and then took their average. TILs staining was scored semi quantitatively using a 3 tiered scale. Results: Forty patients who fulfilled the inclusion & exclusion criteria were included in the study with most common age group being 10 to 19 years (27 patient, 68%). The male: female ratio was 1.6: 1 and the most common location of tumor was distal femur. Majority of patients had the histological subtype of conventional osteosarcoma (37 patients, 92.5%). Lung metastasis was present at time of initial diagnosis in 27 patients (67.5%). At the end of 2 years, 27 patients were alive (60%) while 13 patients had died due to disease. PD-L1 expression was negative in 17.5%, low positive in 15% and high positive in 67.5%. Among TIL category, 19 patients belonged to category 1, 10 belonged to category 2 & 11 belonged to category 3. There was significant correlation between PD-L1 expression score & TIL category. PD-L1 score did not correlate with percentage of necrosis following chemotherapy, metastasis on presentation or overall survival. Conclusions: PD-L1 score had significant correlation with density of Tumor Infiltrating lymphocytes (TIL). However, PD-L1 score did not correlate with overall survival, tumor-free survival, progression of metastasis or local recurrence.