Introduction: Tumors or neoplasms are classified as either benign or malignant, with malignant tumors—commonly referred to as cancer—being particularl
y dangerous due to their ability to spread aggressively. Cancer treatment requires a multidisciplinary approach involving different methods, which are chosen according to the type of cancer, its location and its stage of progression. Radiotherapy is one of the most commonly used forms of local treatment for cancer. The presence of radioresistant cells remains one of the major challenges in radiotherapy. Understanding the mechanisms leading to radioresistance is important to improve treatment efficacy and reduce the risk of resistance development and long-term adverse effects. This thesis provides a comprehensive overview of the mechanisms contributing to radioresistance. Purpose: The aim of this thesis is to present the key mechanisms that enable cancer cells to become radioresistent, explore their interconnections, and highlight potential strategies for enhancing and improving future cancer therapies. Methods: A descriptive approach was used, supported by a systematic literature review. The analysis included freely accessible scientific articles in English, published between 2015 and 2025. Articles were identified using the following keywords: cancer, tumor, radiation resistance, radioresistance, molecular mechanisms, signaling pathways, radiotherapy, radiation therapy. Results: Out of a total of 2001 identified articles, 12 scientific papers were selected for detailed analysis based on predefined inclusion criteria. The selected studies were evaluated based on title, authorship, year of publication, tumor type, described resistance mechanisms, and proposed future treatment strategies. Discussion and conclusion: The most frequently discussed mechanisms of radioresistance include hypoxia, cancer stem cells, the tumor microenvironment, deoxyribonucleic acid damage repair, apoptosis, cell cycle regulation, epithelial–mesenchymal transition, cancer-associated fibroblasts, non-coding ribonucleic acids , and epigenetic mechanisms. In addition, some mechanisms have only been observed in certain types of cancer. All of these processes are closely interconnected through one or more signaling pathways. A deeper understanding of resistance mechanisms is crucial for the development of new therapeutic approaches that could enhance the radiosensitivity of cancer cells, improve treatment outcomes, and contribute to a better quality of life for cancer patients.
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