Evaluation of the impact of pre-operative stereotactic radiotherapy on the acute changes in histopathologic and immune marker profiles of brain metastases

Abstract

The unique acute effects of the large fractional doses that characterize stereotactic radiosurgery (SRS) or radiotherapy (SRT), specifically in terms of antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis on brain metastasis have yet to be empirically demonstrated. The objective of this study is to provide the first in-human evaluation of the acute biological effects of SRS/SRT in resected brain metastasis. Tumor samples from patients who underwent dose-escalated preoperative SRT followed by resection with available non-irradiated primary tumor tissues were retrieved from our institutional biorepository. All primary tumors and irradiated metastases were evaluated for the following parameters: tumor necrosis, T-cells, natural killer cells, vessel density, vascular endothelial growth factor, and apoptotic factors. Twenty-two patients with irradiated and resected brain metastases and paired non-irradiated primary tumor samples met inclusion criteria. Patients underwent a median preoperative SRT dose of 18 Gy (Range: 15-20 Gy) in 1 fraction, with 3 patients receiving 27-30 Gy in 3-5 fractions, followed by resection within median interval of 67.8 h (R: 18.25-160.61 h). The rate of necrosis was significantly higher in irradiated brain metastases than non-irradiated primary tumors (p < 0.001). Decreases in all immunomodulatory cell populations were found in irradiated metastases compared to primary tumors: CD3 + (p = 0.003), CD4 + (p = 0.01), and CD8 + (p = 0.01). Pre-operative SRT is associated with acute effects such as increased tumor necrosis and differences in expression of immunomodulatory factors, an effect that does not appear to be time dependent, within the limited intervals explored within the context of this analysis.

Figure 1

Representative tissue samples displaying the acute effects of stereotactic radiosurgery in brain metastasis. Hematoxylin and eosin staining showing necrosis of a primary tumor (NSCLC) sample (A); primary tissue sections were immunohistochemically stained for CD3 + (B), CD4 + (C), and CD8 + (D) cells. Hematoxylin and eosin staining demonstrated an increase in necrosis in the paired resected brain metastasis after pre-operative SRS (E). Additionally, a decrease in all immunomodulatory cell populations, including CD3 + (F), CD4 + (G), and CD8 + cells (H) were observed on pairwise comparison. (Original magnification × 40).

Figure 2

Relationship for the percentage of tumor necrosis between the primary tumor and irradiated BM: (A) tumor necrosis in primary tumors was significantly lower than irradiated BM; (B) no difference in the proportion of tumor necrosis with respect to time interval from SRT to surgery was observed: primary (non-irradiated), BM < 24 h, 24–48 h, 48–72 h and > 72 h.

Figure 3

Paired box plots representing the immunomodulatory effects of pre-operative stereotactic radiotherapy on metastasis tumors compared to non-irradiated primary tumors on immunomodulatory cells, including CD3 + (T-cell receptor) (A), CD4 + (T helper cell) (B), and CD8 + (cytotoxic T lymphocytes) (C).