Theranostics have been a breakthrough in oncology, offering a dual approach that integrates diagnosis and targeted therapy within a single platform. This advancement has refined personalized medicine, enabling clinicians to visualize tumors, assess their molecular characteristics, and deliver precise treatments tailored to individual patients. Current cancer imaging modalities, including PET, MRI, and CT, have been enhanced by the development of radiopharmaceuticals and nanoparticle-based agents that not only identify malignant tissues with high specificity but also serve as vehicles for therapeutic delivery. So far, various classes of theranostics agents have been reported for solid tumor imaging and therapeutics in combination. Among them, radiolabeled antibodies, peptides, nanoparticles, etc. have gained tremendous attention in treating various cancers, notably in neuroendocrine tumors and prostate cancer. On the other hand, the integration of molecular imaging with theranostics approaches has improved the accuracy of tumor staging, patient stratification, and treatment planning, leading to better outcomes. Such agents augment the real-time monitoring of therapeutic efficacy and early detection of resistance, providing a methodology that can guide treatment adjustments, while minimizing organ toxicity. Despite these advancements, challenges remain, including the need for more robust biomarkers, improved targeting specificity, and the development of agents that can overcome tumor heterogeneity and resistance mechanisms. Herein, various advancements in theranostics enabling precise and effective cancer imaging and therapy have been discussed.