Cancer, a leading cause of death globally, is characterized by uncontrolled cell growth and spread. Current treatments, including surgery, chemotherapy, and radiation therapy, often have limitations in terms of efficacy and side effects. Nanotechnology offers a promising avenue for improving cancer diagnosis and treatment by enabling targeted delivery of therapeutic agents and enhanced imaging capabilities. Magnetic hybrid nanostructures (MHNs), combining magnetic properties with other functionalities, are particularly attractive due to their potential for targeted drug delivery, magnetic resonance imaging (MRI) contrast enhancement, and hyperthermia therapy. This review explores the diverse applications of MHNs in cancer theranostics, focusing on their unique properties and potential advantages over conventional methods. The increasing use of MHNs in various cancer treatments and diagnostic tools is driven by the need for more precise, effective, and less invasive therapies with reduced side effects. The ability to tailor the properties of MHNs by adjusting size, shape, composition, and surface functionalization is key to their versatility in both diagnosis and treatment modalities. The integration of artificial intelligence (AI) in the design, optimization, and application of MHNs further enhances their capabilities and promises to revolutionize cancer care. The combination of nanotechnology and AI opens exciting new avenues for personalized medicine, allowing for more targeted and effective treatment strategies tailored to individual patients.

The literature extensively documents the use of various nanomaterials in cancer treatment and diagnosis. Polymer-based nanoparticles, such as those made from poly(lactic-co-glycolic acid) (PLGA), poly(glycolic acid) (PGA), and poly(lactic acid) (PLA), have been explored due to their biocompatibility and biodegradability. Magnetic nanoparticles, especially iron oxide nanoparticles (e.g., superparamagnetic iron oxide nanoparticles, SPIONs), have attracted significant attention because of their magnetic properties enabling targeted drug delivery and MRI contrast enhancement. Carbon-based nanomaterials, including graphene and carbon nanotubes, are being investigated for their high surface area and ability to carry therapeutic agents. Noble metals like gold, silver, and palladium offer unique optical and therapeutic properties. Semiconducting nanomaterials, such as quantum dots, provide fluorescence capabilities for imaging. Furthermore, numerous studies have examined biomolecule conjugation, particularly with genetic materials (DNA and RNA) or proteins, to enhance targeting and functionality. These studies laid the groundwork for the development and exploration of magnetic hybrid nanostructures, combining these various features for enhanced efficacy.

The review followed a systematic approach to collect relevant literature. Databases such as PubMed, Web of Science, Scopus, and Google Scholar were searched using keywords such as "magnetic nanoparticles," "cancer theranostics," "drug delivery," "magnetic resonance imaging," "hyperthermia," "photothermal therapy," "photodynamic therapy," and various combinations thereof. Articles focusing on the design, synthesis, characterization, and applications of MHNs in cancer were included. The selection criteria encompassed in vitro and in vivo studies, pre-clinical and clinical trials, as well as review articles. The selected articles were critically analyzed to extract information on the types of MHNs, their synthesis methods, characterization techniques, applications in diagnosis and therapy, and limitations. This systematic approach ensured comprehensive coverage of the relevant literature and allowed for a structured and detailed presentation of the findings. The information gathered was organized according to the various types of MHNs, their applications in cancer diagnosis and therapy, and the emerging role of AI. The review provides details on the different strategies for MHN synthesis, the characterization techniques used to assess their properties, and the mechanisms by which they function in cancer therapy and diagnosis. The data presented is supported by relevant figures and tables from various publications included in the review, strengthening the factual basis of the findings. This comprehensive review aimed to consolidate the current knowledge on this rapidly evolving field, highlighting both the successes and the challenges of using MHNs in cancer theranostics.

The review highlights several key findings. MHNs, with sizes above 10 nm, are effective as T2-weighted MRI contrast agents while MHNs smaller than 5 nm act as effective T1-weighted MRI contrast agents. The size and surface functionalization of MHNs are critical for optimizing their performance in MRI. Different types of MHNs, including polymer-magnetic, carbon-magnetic, noble-metal-based magnetic, semiconducting fluorescent magnetic, and biomolecular conjugates, exhibit promising results in various applications. In cancer diagnosis, MHNs are used in MRI, magnetic fluorescent imaging probes, magnetic biochips, and magnetic biosensors. For cancer therapy, MHNs have been successful in chemotherapy drug delivery, stimuli-responsive drug delivery (pH and temperature sensitive), hyperthermia, photothermal and photodynamic therapies, and magnetic nanorobot applications. Ferrites (e.g., ZnFe2O4) exhibit high magnetic susceptibility and are suitable for drug delivery and hyperthermia. Artificial intelligence (AI) is emerging as a powerful tool for optimizing MHN design, synthesis, and application, enhancing the prediction of hyperthermia treatment outcome, assisting in drug delivery and toxicity assessment, and enabling personalized treatment strategies. AI also improves the performance of diagnostic methods like MRI and biosensors, thereby improving the speed and accuracy of cancer detection. The application of AI in this context includes predictive modeling, targeted drug delivery optimization, real-time monitoring of patient responses, adverse event prediction, and improved image analysis. These AI-driven advancements offer significant potential for improving the efficacy and precision of cancer diagnosis and treatment.

The findings of this review demonstrate the significant potential of MHNs for revolutionizing cancer theranostics. The ability to combine magnetic properties with diverse functionalities provides a versatile platform for both diagnostic and therapeutic applications. The size-dependent behavior of MHNs in MRI is critical for optimizing their contrast enhancement, highlighting the need for precise control over nanoparticle synthesis. The successful application of MHNs in various drug delivery strategies, hyperthermia, and phototherapies underscores the advantages of targeted therapies in improving treatment efficacy while reducing side effects. The integration of AI represents a major advancement, enabling the optimization of MHN properties and the development of personalized treatment plans. While promising, the field still faces challenges, particularly regarding toxicity and long-term effects. Further research on optimizing biocompatibility, ensuring efficient and controlled drug release, and addressing potential toxicity issues is needed. Future directions should explore the synthesis of more biocompatible and biodegradable MHNs, develop advanced AI algorithms for personalized treatment optimization, and conduct large-scale clinical trials to validate the clinical efficacy and safety of these promising nanostructures.

This review showcases the remarkable progress made in developing and applying MHNs in cancer theranostics. Their versatility in both diagnosis and therapy, coupled with the increasing integration of AI, promises to significantly improve cancer treatment outcomes. Future research should focus on addressing the remaining limitations, including toxicity and long-term effects, to translate these promising nanostructures into widely available clinical tools. The convergence of nanotechnology and AI holds great potential for personalized medicine and the development of more effective and patient-specific cancer treatments.

While this review provides a comprehensive overview, certain limitations exist. The focus is primarily on preclinical studies and a limited number of clinical trials, implying that further clinical validation is necessary. The review heavily relies on data from published literature, and variations in methodologies and experimental conditions across different studies might affect the generalizability of some findings. A thorough assessment of the long-term toxicity and environmental impact of MHNs requires more extensive research and careful consideration of the long-term effects of these materials on human health and the environment. Moreover, some publications included are from less-renowned or relatively new journals, thus affecting the overall quality and reproducibility of the findings.