Cancer is one of the main causes of death worldwide. Chemotherapy, radiotherapy and surgery are currently the treatments of choice for cancer. However, conventional therapies have their limitations, such as non-specificity, tumor recurrence and toxicity to the target cells. Recently, nanomaterials have been considered as therapeutic agents against cancer. This is mainly due to their unique optical properties, biocompatibility, large surface area and nanoscale size. These properties are crucial as they can affect biocompatibility and uptake by the cell, reducing efficacy. However, because nanoparticles can be functionalized with biomolecules, they become more biocompatible, which improves uptake, and they can be specifically targeted against cancer cells, which improves their anticancer activity. In this review, we summarize some of the recent studies in which nanomaterials have been functionalized with the aim of increasing therapeutic efficacy in cancer treatment.