The distinct luminescent, magnetic characteristics and unique optical properties such as narrow emission bands, emission tunability, multiple emission wavelengths, long fluorescence lifetime, and large Stokes shift of lanthanide ions (Ln3+) make multifaceted lanthanide-based nanoparticles (NPs) predicted to have a significant influence in nanomedicine as well as growing in prominence for usage in a multitude of theranostic applications. Numerous imaging techniques have been extensively used in conjunction with probes that can increase the contrast between normally healthy and malignant tissues to identify malignancy and its pathological activities. Because of the compartmentalised framework, nanoassemblies present an intriguing prospect for cancer multidimensional imaging and theranostics. This allows for the combination of diagnosis and therapy on a single platform, facilitating biological system investigations, molecular imaging, and therapeutic monitoring.