Analysis of the immune infiltrate in undifferentiated pleomorphic sarcoma of the extremity and trunk in response to radiotherapy: Rationale for combination neoadjuvant immune checkpoint inhibition and radiotherapy

Abstract

Background: Undifferentiated pleomorphic sarcoma of the extremity and trunk (ET-UPS) presents a unique therapeutic challenge. Although immunotherapy has recently been employed in advanced soft tissue sarcoma, there is limited data characterizing the immune infiltrate in ET-UPS. Radiotherapy (RT) has been shown in other tumor types to promote tumor antigen release and enhance tumor-specific targeting by the adaptive immune system. The aim of this study was to 1) characterize the baseline immune infiltrate and 2) evaluate the effect of preoperative RT on the histologic appearance of and the immune infiltrate in ET-UPS. Methods: We identified 17 matched ET-UPS samples before and after RT. Immunohistochemistry was performed with CD8, CD4, PD-L1, PD1, CD3, CD163 and FoxP3 positive cells identified in all samples. Changes in the immune infiltrate following RT were examined. Results: There was a trend towards increased density of tumor infiltrating immune cells in ET-UPS following RT, with increases in median number of CD3 (158 vs 219 cells/mm², p = 0.06), CD4 (3 vs 13 cells/mm², p = 0.01), CD8 (55 vs 111 cells/mm², p = 0.17), and FOXP3 (14 vs 25 cells/mm², p = 0.23) positive cells. Interestingly, although PD-L1 was not expressed in any ET-UPS tumor at baseline, positive PD-L1 expression was observed in 21% (3/14) of tumors after RT (p = 0.07). Conclusion: An immune infiltrate is present in ET-UPS at the time of diagnosis, with a trend towards increased density of immune infiltrate and PD-L1 expression after RT. These data support prospectively evaluating immune checkpoint inhibitors with standard of care RT in the treatment of ET-UPS.

Keywords: extremity sarcoma; immune check point; immunotherapy; radiation therapy; undifferentiated pleomorphic sarcoma.

Figure 1.

Examples of treatment effect following radiotherapy of undifferentiated pleomorphic sarcoma. Representative photographs of H+E stained undifferentiated pleomorphic sarcoma of the extremity and trunk demonstrating increased tumor necrosis and hyalinization following radiotherapy. (A) Tumor with extensive hyalinization (H&E, 100x). (B) Tumor with extensive necrosis with ghost and degenerative tumor cells (H&E, 100x). (C) Tumors could also have a mix of both necrosis and hyalinization (H&E, 100x). Cytological changes consistent with treatment effect (inset, H&E, 200x) was also present in this sample.

Figure 2.

Association between treatment effect following radiotherapy and survival. Increased hyalinization (A) and decreased necrosis (B) of undifferentiated pleomorphic sarcomas following radiotherapy are associated with improved recurrence-free and overall survival following surgical resection.

Figure 3.

Comparison of immune infiltrate immunohistochemical studies in a pre- and post-treatment undifferentiated pleomorphic sarcoma. Representative photographs of immunostained undifferentiated pleomorphic sarcoma of the extremity and trunk. Increased CD3, CD4, CD8, CD163, FOXP3 and PD1 positive cells were seen in the post treatment specimen. Tumoral PD-L1 expression was increased.

Figure 4.

Quantification of the change in the immune infiltrate following radiotherapy of undifferentiated pleomorphic sarcomas of the extremity and trunk. (A) Median CD3, CD8, CD4, FoxP3, and PD-1 positive cells prior to and following radiotherapy; (B) change in the number of CD3 positive tumor infiltrating cells, paired samples by patient; (C) change in the number of CD8 positive tumor infiltrating cells, paired samples by patient; (D) change in the number of CD4 positive tumor infiltrating cells, paired samples by patient.