Preoperative Radiosurgery on Early Breast Cancer Patients: Analysis of Tumor Genetic Background and Tumor Immune Microenvironment.

A phase II trial was conducted to assess the feasibility, safety, and activity of a single 21 Gy preoperative robotic radiosurgery (prRS) in early breast cancer patients, 50+ years old, hormonal receptors positive/human epidermal growth factor receptor 2 negative (HR+/HER2-), sized up to 25 mm. Breast surgery was performed 2 to 4 weeks after radiosurgery. A translational study was carried out to explore the modulation of tumor-immune microenvironment before and after irradiation and the transcriptome on tumor samples before irradiation. Among the 70 patients recruited, 22 patients were successfully treated with prRS. Fresh pre-treatment tumor biopsies and fresh post-radiosurgery and post-operative tumor samples were retrieved. For immunohistochemistry analysis, pre-radiosurgery biopsies and post-operative tumors were stained with specific antibodies to evaluate the expression of different immune-related biomarkers. For the transcriptome analysis, total RNA was extracted from frozen pre-treatment samples and RNA sequencing was performed by using a total of 10 ng/uL. The statistical analyses aiming at detecting differences in gene expression according to tumor downstaging were conducted by fitting age-adjusted linear regression models, and applying the false discovery rate (FDR) method for correcting for multiple tests. As clinical output, we considered tumor downstaging according to pTNM and patients were classified as Radio-Responders (R-R = 8) and non-Radio-Responders (nR-R = 13) after prRS. IHC was performed on available 19 pairs of pre- and post-irradiation tissues for evaluation of CD68, CD163, CD4, CD8, CD56 and CD16: preliminary analysis showed a marked increase in CD68, CD163 and CD4 staining after tumor prRS. RNAseq results showed 170 differentially expressed genes between R-R and nR-R. Statistical analysis identify CCDC97 and MDIFC as genes that were significantly up- and down-regulated respectively in R-R patients. CCD97 is an orphan gene previously described as part of a nuclear interactome with functional role in DNA damage repair, while MDFIC is reported to be associated with pro- or anti-tumoral functions as chemoresistance induction or cell proliferation inhibition. The phase II trial enrolled 22 patients; this little number limits the statistical power of results obtained in the translational analysis. Based on the preliminary results, IHC analysis showed that prRS modulates the immune microenvironment composition in early breast cancer patients. Furthermore, we hypothesized that the differential expression of CCDC97 and MDFIC may play a role in prRS response. The role of orphan genes CCDC97 and MDFIC in response to radiation and to hypofractionation makes worthy further pre- and clinical investigations. [ABSTRACT FROM AUTHOR]