This paper has been accepted for publication at the 2023 International Conference on Robotics and Automation. Abstract-- In this paper, we present the design, fabrication, and evaluation of a novel flexible, yet structurally strong, Concentric Tube Steerable Drilling Robot (CT-SDR) to improve minimally invasive treatment of spinal tumors. Inspired by concentric tube robots, the proposed two degree-of-freedom (DoF) CT-SDR, for the first time, not only allows a surgeon to intuitively and quickly drill smooth planar and out-of-plane J-and U-shape curved trajectories, but it also, enables drilling cavities through a hard tissue in a minimally invasive fashion. We successfully evaluated the performance and efficacy of the proposed CT-SDR in drilling various planar and out-ofplane J-shape branch, U-shape, and cavity drilling scenarios on simulated bone materials. Bone is the most common site of metastatic disease after lung and liver [1], [2] and one of the most common causes Figure 1: Conceptual illustration of the proposed CT-SDR, of chronic pain among cancer patients [1], [2].