Effect of Stereotactic Ablative Radiation Therapy (SABR) on Peripheral Lymphocyte Subsets in 20 Cancer Patients

Abstract

Abscopal effect reveals that local radiotherapy enhances systemic antitumor immune response, especially for stereotactic ablative radiotherapy (SABR). And the mechanism remains unclear. In this research, we retrospectively investigated the dynamic change of lymphocyte subsets in the patients treated with SABR. We analyzed the data from 20 cancer patients with I-IV clinic stage who underwent SABR. The tumor types covered urinary system tumor (n=9), non-small cell lung cancer (n=5), hepatobiliary cancer (n=2), head and neck cancer (n=1), soft tissue sarcoma (n=1), ovarian cancer (n=1) and thymic carcinoma (n=1). Twenty-five percent (4 in 20) of the gross tumors were in I-III clinic stage and 75% (16 in 20) were metastatic lesions or relapse lesions. The radiation treatment (RT) delivered SABR combined or not combined with convention fraction radiotherapy(CFRT). All of the 20 patients had peripheral lymphocyte subsets tests at the start of RT (pretreatment or within 1 week after the first radiation). Seventeen of them had the same tests at the end of RT (within 1 week after the last radiation) and 13 did it after RT (in 1-3 months after the last radiation). Paired t test was used to evaluate statistical significances. The median age of 20 patients was 67 (range 40-92). The patients received SABR with 12-70Gy/2-10 fractions (median 24Gy, median 4 fractions) and following convention fraction radiotherapy (CFRT) with 0-52Gy/0-26 fractions (median 45.45Gy, median 20.5 fractions). The biological effective dose was median 100.85 Gy (range 79.20-186.08Gy) in the center of the tumors. In the comparison of the peripheral lymphocyte subsets at the start of RT and the end of RT, we found peripheral T cells, B cells and NK cells were significantly decreased at the end of RT (P =0.000, P =0.000, P =0.002). In contrast, the proportions of CD3+/CD8+ T cells, CD3+/CD4+ T cells and CD4+/CD8+ ratio did not differ at the start of RT and at the end of RT. The results showed that the proportion of CD3+/CD8+ T cells was significantly increased after RT compared with the start of RT (mean 50.60% vs.41.37%, P =0.044). In addition, compared with the start of RT, the proportion of CD3+/CD4+ T cells was significantly decreased (mean 46.15% vs.57.21%, P =0.041) and also the CD4+/CD8+ ratio (mean 1.03 vs.1.53, P =0.045). There were no significant differences in peripheral T cells, B cells and NK cells after RT compared with the start of RT. Increased T cells (P =0.031), increased proportion of CD3+/CD8+ T cells (P =0.043) and decreased proportion of CD3+/CD4+ T cells (P =0.049) were found after RT compared with the end of RT. Stereotactic ablative radiotherapy (SABR) has dynamic impact on the proportion of T cells subsets, particularly CD3+/CD8+ T cells involved. SABR may have a prolonged and effective impact on systemic antitumor immune response.