Malignant tumors have the capability to metastasize and colonize, meaning that they can spread to other organs and tissues, distributing metastatic focus and are hard to target. Although significant advances have been made in cancer treatment, it remains one of the leading causes of death around the globe. In recent years, new-emerging implantable systems and devices have been developed to tackle the challenge of metastatic tumors. In this review, implantable systems for suppressing tumors and preventing tumor recurrence are reported. In particular, we emphasize the responsive drug delivery systems and the external field assisted catalytic therapy for tumor treatment, as well as implantable biosensors for tumor microenvironment monitoring. We also conclude the open challenges and future perspectives of implantable systems and devices for cancer therapy and sensing.