Tumor Infiltrating Lymphocytes May Predict for Distant Metastasis in Soft Tissue Sarcomas

Abstract

The presence of tumor infiltrating lymphocytes (TILs) has been shown to be prognostic in malignancies such as breast, ovarian and colorectal cancer. Moreover, hypofractionated radiation therapy (RT) has been shown to improve tumor control and lead to an increased number of TILs in tumors. However, the significance of TILs in soft tissue sarcoma (STS) remains to be determined. In this study, we aim to determine if TILs are prognostic in patients undergoing pre-operative RT for STS of the extremity and chest-wall, and to evaluate if hypofractionated RT is associated with increased TILs when compared to standard fractionation. H&E slides from resected specimens of extremity and trunk STS patients who underwent pre-operative standard fractionation at 2 Gy/fx or hypofractionation at 7 Gy/fx were reviewed by a blinded pathologist to quantify TILs. All hypofractionated patients were enrolled on an institutional clinical trial. TILs were defined as lymphocytes infiltrating in areas of viable tumor cells. TILs were quantified utilizing 40x and 10x objectives lens (Olympus BX40 microscope) at the tumor hot spots (areas of tumors with highest concentration of TILs) and expressed as a percentage; TILs%/ 40x and TILs%/ 10x. Receiver-operating curve (ROC) analysis was performed to assess the best cut-off that predicted for distant metastasis (DM) in patients undergoing pre-operative RT. Distant metastasis-free survival (DMFS) was calculated using Kaplan-Meier survival analysis. A t-test was performed to assess the difference in means between the 2 groups. Seventy-nine patients with stage I-III STS of the extremity and chest-wall were analyzed, 61 who underwent standard and 18 who underwent hypofractionated RT. Median overall age was 56. Median overall tumor size was 9.8 cm. Median dose of the standard and hypofractionated groups were 50 Gy and 35 Gy, respectively. 30% of patients developed DM in the standard fractionated group vs 11% in the hypofractionated group (p=0.07). The median overall % TILs at 10x and 40x was 20% and 25%, respectively. The mean % TILs at 10x and 40x for the standard and hypofractionated RT was 19.68% vs 31% (p=0.06) and 26.2% vs 42.8% (p=0.03), respectively. ROC analysis revealed that % TILs (10x and 40x) ≤10 was associated with increased risk of distant metastasis (p<0.0001). Median DMFS for patients with % TILs ≤10 was 44.3 months vs >54 months for % TILs > 10% (p=0.0009). In localized STS of the extremity and chest-wall, increasing % TILs was associated improved DMFS. Hypofractionated RT appears to be protective with these patients demonstrating higher % TILs and a decreased rate of developing DM. A cut-off ≤10 % TILs of was shown to be associated with poorer DMFS in this study for all patients treated with pre-operative RT. Further validation of the clinical utility of TILs in this context is warranted.