1. Introduction

Osteosarcoma (OS) is a rare mesenchymal tumour [1] and the most common primary malignant bone tumour in adolescents and young adults [2]. Despite the innovations in molecular medicine in recent decades, there has been little progress in the treatment of OS for over 30 years [3]. When the disease is localized, the surgical resection of the primary tumour and multiagent chemotherapy (e.g., high dose methotrexate, adriamycin, and cisplatin with or without ifosfamide) allows for a cure rate of 60–70% ^[1][2][4][1,2,4]. When the disease presents metastases by the time of diagnosis or in the case of relapsed disease, the prognosis for the patient is poor, and the survival rate is lower than 30% at 5 years ^[1][2][4][5][1,2,4,5].

Despite the consensus on the first line treatment of patients with systemic regimens, when recurrence or progression occurs, there is no international agreement on the best therapy for OS patients [6]. With the exception of the benefits of a surgical complete remission (second or subsequent) ^[4][5][6][4,5,6], there continues to be an ongoing debate regarding the efficacy of systemic treatments ^[4][5][6][4,5,6] and there is a lack of efficient treatment options for patients with advanced and relapsed OS.

The availability of Next Generation Sequencing (NGS) techniques has completely revolutionized clinical research, as well as basic and applied medicine over the last decade [7]. NGS is a high-throughput sequencing technology that is able to precisely map the entire genome of an individual in a few hours with a limited cost [8]. NGS approaches include whole genome sequencing, exome sequencing, transcriptome sequencing, and RNA sequencing ^[8][9][8,9]. These methodologies have facilitated the analysis of genomic profiles in cancer patients improving our understanding of the disease ^[7][9][7,9]. The tumour sequencing and its matched normal counterpart has the potential to reveal a range of genetic alterations with significant implications for clinical practice in terms of diagnosis, prognosis and subsequent treatment choices [10]. Indeed, NGS allows the identification of tumour specific aberrations with the potential either to discover new prognostic biomarkers or to offer potential information for new personalized treatments, thus improving the precision medicine concept especially for patients with a relapsed/refractory disease ^[7][10][7,10].

The development of precision medicine trials (PMTs) has improved as a result of the knowledge that the genomic profile of a patient’s tumour can be precisely mapped and matched, when possible, to a targeted therapy in real time [3]. Initially, PMTs were most common for adult malignancies, especially for the most frequent neoplasms. Thereafter, there was a gradual interest in expanding this personalized approach to rare tumours such as paediatric tumours, including OS ^[3][11][3,11].

So far, standard clinical trial approaches for relapsed or advanced OS patients showed a lack of efficacy ^[1][2][6][1,2,6]. The identification of specific genomic targets for OS patients is essential for better stratification of the patients enrolled in future matched clinical trials [12].

It is now widely accepted that OS patients may benefit from a deep comprehensive molecular genomic sequencing approach ^[3][13][3,13]. Nevertheless, this kind of treatment approach is in its infancy, and there are several obstacles to overcome for OS patients as described below.

2. Oncological Precision Medicine Trials

Several oncology studies have evaluated the feasibility and use of genomic-driven precision medicine in tumours in recent years.

Molecular Analysis for Therapy CHoice (MATCH) is a precision medicine treatment clinical trial for adult and paediatric patients supported by the National Cancer Institute (NCI) and by the Children’s Oncology Group (COG). The trial has an umbrella design with treatment rules based on the presence of a molecular aberration ^[11][14][15][11,14,15]. This study seeks to determine the response rate in adult and paediatric patients with advanced and relapsed solid tumours harbouring genomic alterations that can be treated with available drugs [11]. Following the same principles, further PMTs have been established along the same lines, including some for paediatric patients (Table 1).

PMTs usually consist of three phases. The first phase includes sample collection (especially tumour biopsies), the preparation of biological materials, and the generation of all required genomic data. As a result of these, each tumour of all enrolled patients is univocally associated with a precise molecular profile. During the second phase, genomic data is assessed by an expert multidisciplinary board to evaluate their clinical relevance. This panel of experienced clinicians evaluates the genomic alterations of each tumour considering their biological relevance, their potential therapeutic targeting with available compounds, and their link with the medical history of the patient. These evaluations are necessary for a rapid translation into a clinical decision making. Therefore, whenever possible, the enrolment of the patient into a genomic-driven treatment trial is encouraged.

The second phase aims at identifying the genomic alterations that are relevant for tumour growth and progression that could be selected for a targeted therapy. This clinical research employs computational algorithms able to prioritize the potentially druggable alterations identified from NGS data. In this light, Worst and colleagues developed a work-flow able to rank genomic alterations in seven levels of increasing clinical relevance (e.g., from “very high” to “very low”) on the basis of their effect on the encoded protein, the availability of a direct targeting drug, and literature evidences of possible pathway activation ^[16][17]. In the INFORM pilot study, patients with a very high priority target alterations (e.g., ALK, BRAF, and NRAS mutations, and MET and NTRK-fusions) showed an improvement in the Progression-Free Survival (PFS) ^[17][18]. Indeed, the median PFS in paediatric patients with a high priority genomic alteration treated with the matched drug was significantly higher compared to that of all patients with no druggable aberration (i.e., 204.5 and 114 days, respectively—p = 0.0095) ^[17][18]. Hence, a promptly identification of patients whose tumours are harbouring a high priority target genomic alteration is necessary to better address the physician’s treatment choice.

The preliminary results of the genomic-driven precision medicine trials, despite being promising, also presented us with a two-sided challenge. Firstly, the results showed that feasible access to a genomic program to identify somatic targeted alterations is necessary. This can be achieved with a specialized team to translate the obtained genomic results into reasonable clinical action for those patients [8]. Moreover, the availability of molecular targeted drugs is necessary, especially for more vulnerable populations such as paediatric patients or patients with a rare oncological disease, including OS patients. Recent advances in our understanding of molecular oncogenesis allowed for the stratification of malignancies into molecularly similar tumours, both within and across the tissue of origin, thus leading to the establishment of improved therapeutic treatments ^[18][27]. This strongly suggests that the development of targeted therapies can be better informed by tissue agnostic clinical trials, which represent a significant paradigm shift in precision medicine for cancer patients ^[18][27].

3. Osteosarcoma: The Challenges for Successful PMTs

OS patients represent a minority of patients that have been enrolled into PMTs so far (Table 1). This low enrolment rate is due to some challenges that prevent us from fully exploiting the beneficial impact of PMTs on OS patient quality of life. In the following paragraphs, we will discuss three important hurdles for a successful OS PMTs: (1) The modest incidence rate of this rare tumour [9], (2) the technical issues to manage genomic materials from a difficult tissue of origin (i.e., bone) [8], and (3) the highly heterogenous genomic complexity of OS samples ^{[8][19][20][21]}[8,28,29,30].