Citation: Twenhafel, L.; Moreno, D.; Punt, T.; Kinney, M.; Ryznar, R. Epigenetic Changes Associated with Osteosarcoma: A Comprehensive Review. Cells 2023, 12, 1595. https://doi.org/10.3390/ cells12121595 Academic Editor: Kyu Yun Jang Received: 16 April 2023 Revised: 7 June 2023 Accepted: 8 June 2023 Published: 9 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). cells Review Epigenetic Changes Associated with Osteosarcoma: A Comprehensive Review Luke Twenhafel 1, *, DiAnna Moreno 1 , Trista Punt 1 , Madeline Kinney 1 and Rebecca Ryznar 2 1 College of Osteopathic Medicine, Rocky Vista University, Englewood, CO 80112, USA; dianna.moreno@co.rvu.edu (D.M.); trista.punt@co.rvu.edu (T.P.); madeline.kinney@co.rvu.edu (M.K.) 2 Department of Biomedical Sciences, Rocky Vista University, Englewood, CO 80112, USA; rryznar@rvu.edu * Correspondence: luke.twenhafel@co.rvu.edu Abstract: Osteosarcoma is the most common malignant primary bone tumor in children and ado- lescents. While clinical outcomes have improved, the 5-year survival rate is only around 60% if discovered early and can require debilitating treatments, such as amputations. A better under- standing of the disease could lead to better clinical outcomes for patients with osteosarcoma. One promising avenue of osteosarcoma research is in the field of epigenetics. This research investigates changes in genetic expression that occur above the genome rather than in the genetic code itself. The epigenetics of osteosarcoma is an active area of research that is still not fully understood. In a narrative review, we examine recent advances in the epigenetics of osteosarcoma by reporting biomarkers of DNA methylation, histone modifications, and non-coding RNA associated with dis- ease progression. We also show how cancer tumor epigenetic profiles are being used to predict and improve patient outcomes. The papers in this review cover a large range of epigenetic target genes and pathways that modulate many aspects of osteosarcoma, including but not limited to metastases and chemotherapy resistance. Ultimately, this review will shed light on the recent advances in the epigenetics of osteosarcoma and illustrate the clinical benefits of this field of research. Keywords: osteosarcoma; epigenetics; DNA methylation; histone modification; non-coding RNA 1. Introduction Osteosarcoma (OS) is a malignant primary bone tumor originating from mesenchymal cells that produce an immature bone known as an osteoid [1]. It is the most common malignant bone tumor in children and young adults and has a second peak incidence in the elderly [2]. Primary tumors occur at sites of bone growth, such as the metaphysis of long bones, such as those around the knee and shoulder. A minority of cases originate from the pelvis or locations in the axial skeleton, such as the skull and jaw [2]. OS is typically treated with pre- and postoperative chemotherapy and surgical resection of the tumor, including amputation if necessary [3]. Despite aggressive therapy, OS has a relatively poor prognosis, with a 60–70% 5-year survival rate for localized disease. Part of its poor prognosis is due to OS’s propensity for metastasis. Twenty percent of patients present with metastasis, most commonly to the lungs. For these patients, the 5-year survival rate is a frighteningly low 30% [1]. Despite advances in research, OS survival rates have not drastically improved in 30 years. This lack of progression opens the door for different approaches to OS research and treatment. In modern medicine, cancer has been intrinsically linked to genetics. Researchers have identified links between various types of cancer and specific mutations, inheritance patterns, and carcinogens. The genetic origins of OS are not fully understood, but most cases are sporadic. Additionally, connections to OS occurrence have been made with radiation therapy, inherited cancer syndromes, such as familial retinoblastoma and Li Fraumeni syndrome, and bone disorders, primarily Paget’s disease [4,5]. Despite advances Cells 2023, 12, 1595. https://doi.org/10.3390/cells12121595 https://www.mdpi.com/journal/cells