SNPs in DNA repair or oxidative stress genes and late subcutaneous fibrosis in patients following single shot partial breast irradiation

Journal of Experimental & Clinical Cancer Research SNPs in DNA repair or oxidative stress genes and late subcutaneous fibrosis in patients following single shot partial breast irradiation Elisabetta Falvo 0 Lidia Strigari 2 Gennaro Citro 0 Carolina Giordano 1 Genoveva Boboc 1 Fabiana Fabretti 1 Vicente Bruzzaniti 2 Luca Bellesi 2 Paola Muti 4 5 Giovanni Blandino 3 Paola Pinnar 1 0 Laboratory of Pharmacokinetic/Pharmacogenomic, Regina Elena National Cancer Institute , Rome , Italy 1 Department of Radiation Oncology, Regina Elena National Cancer Institute , Rome , Italy 2 Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute , Rome , Italy 3 Translational Oncogenomic, Regina Elena National Cancer Institute , Rome , Italy 4 Department of Public Health, Harvard University , Boston, MA , USA 5 Department of Oncology Juravinski Cancer Center, McMaster University Hamilton , Hamilton, ON , Canada Background: The aim of this study was to evaluate the potential association between single nucleotide polymorphisms related response to radiotherapy injury, such as genes related to DNA repair or enzymes involved in anti-oxidative activities. The paper aims to identify marker genes able to predict an increased risk of late toxicity studying our group of patients who underwent a Single Shot 3D-CRT PBI (SSPBI) after BCS (breast conserving surgery). Methods: A total of 57 breast cancer patients who underwent SSPBI were genotyped for SNPs (single nucleotide polymorphisms) in XRCC1, XRCC3, GST and RAD51 by Pyrosequencing technology. Univariate analysis (ORs and 95% CI) was performed to correlate SNPs with the risk of developing G2 fibrosis or fat necrosis. Results: A higher significant risk of developing G2 fibrosis or fat necrosis in patients with: polymorphic variant GSTP1 (Ile105Val) (OR = 2.9; 95%CI, 0.88-10.14, p = 0.047). Conclusions: The presence of some SNPs involved in DNA repair or response to oxidative stress seem to be able to predict late toxicity. Trial Registration: ClinicalTrials.gov: NCT01316328 Radiotherapy; Breast cancer; Polymorphisms; Late effects; Fibrosis - Background Conservative surgery followed by adjuvant radiotherapy (RT) to whole breast has become widely accepted as a standard of care for women with early breast cancer. In particular, a number of studies [1-4] reported that most (81%-100%) intra breast tumour recurrences after breast conserving surgery (BCS) occur in close proximity to the tumour bed, so providing the rationale of Partial Breast Irradiation (PBI) an adjuvant RT limited to the Index Area i.e. the area of breast only including the primary tumour bed and the surrounding tissue. In addition, the delivery of radiation dose to smaller target volume by PBI is expected to reduce radiation-related toxicity. Thus, the so-called Accelerated Partial Breast Irradiation (APBI), where only the Index Area is irradiated in 1-10 fractions at high dose/fraction, has been promoted in phase I-III trials designed to test feasibility and equivalence with standard Whole Breast Irradiation (WBI) in properly selected low risk early breast cancer patients after BCS [5]. However, a remarkably high rate of late toxicity has been reported by some Authors a few years after follow up with this APBI approach [6,7]. A high late toxicity rate was also observed in our cohort, after single shot of PBI (SSPBI) [8]. Thus the possibility to predict patient outcome based on marker genes correlated with radio-induced toxicity was investigated. The interaction of RT with living tissue generates, directly or transitorily, reactive oxygen species (ROS) triggering a series of inflammation reactions. Adaptation to oxidative stress occurs by activating genes that characterize the cellular responses to this type of stress and generates a series of processes including DNA repair pathways, cell cycle arrest, antioxidant enzymes and secretion of cytokines that are suspected to play a central role in the development of mainly late normal tissue damage [9,10]. These mechanisms, eventually lead to avoiding extensive DNA damage, cell death [11], and inflammatory process, that may enhance ROS production, thus, contributing to the formation of fibrogenesis and tissue remodelling [12]. In particular, GlutathioneS-Transferase (GSTs) are antioxidant enzymes which are classified into the following classes: alpha (GSTA), mu (GSTM), pi (GSTP), theta, sigma, and kappa. Under conditions of stress the GSTP1 class is implicated in proapoptotic signalling and may mediate cytotoxicity [13-15]. Two independent studies recently carried out on BC patients have reported a significant association between the GSTP1 105Val variant (313 G) and an increased risk of developing acute or late adverse reactions induced by radiation therapy [9,16]. In addition, XRCC1 (X-ray Repair Cross-Complementation group 1), XRCC3 (X-ray Repair Cross-Complementation group 3) RAD51, genes involved in the DNA repair process may influence susceptibility to side effects in patients receiving radiation therapy given that DNA is a direct target for ionizing radiation [17-20]. Various studies [21-23] showed a significant association between the polymorphic nature of these genes and the possibility of developing biomarkers or predictive assay for radio-sensitivity in breast cancer patients. To correlate the genetic variation and association between the development of late effects [24,25], we investigated the following specific polymorphic genes: XRCC1 (Arg399Gln), XRCC3 (5UTR and Thr241Met), GSTP1 (Ile105Val) and RAD51. Methods From March 2006 to January 2008, patients who underwent BCS and a sentinel node biopsy and/or axillary dissection for early breast adenocarcinoma and met eligibility criteria were treated in the prone position with an adjuvant single dose 3D-CRT APBI schedule to the Index Area. The eligibility criteria included being aged 48 years with a life expectancy of at least 5 years, postmenopausal status, histologically proved cancer, non lobular, adenocarcinoma of the breast, primary tumours 3 cm, negative surgical margins ( 2 mm), negative sentinel nodes or < 4 positive axillary nodes, no extracapsular extension, no previous radiotherapy. The exclusion criteria included patients with multicentric disease, extended intraductal component (EIC > 25%), Pagets disease of the nipple, lobular adenocarcinoma, and distant metastases. A dose of 18 (in 4 patients) or 21 Gy (in 60 patients), normalized to the PTV mean dose, was prescribed in a single session. Major technical details of our approach have been previously reported in detail in a distinct paper [26]. Some radiobiological considerations on single dose, time factors, clonogenic cell density and dose constraints are reported in distinct papers [27-30].The study was conducted in accordance with the Helsinki Declaration. Each patient was informed about the study protocol in both verbally and in writing (informed consent) in advance. (...truncated)