Metasurface biosensors have become the core label-free and rapid-detection technology in bioanalysis. Lung cancer and brain cancer are the first leading causes of cancer death among adults and adolescents, respectively, where poor early diagnosis results from expensive detection costs and time consumption. To tackle the above problems, here, we introduce a terahertz-domain metasurface biosensor for cancer diagnosis, relying on a perfectly symmetrical periodic surface structure, which significantly exhibits polarization-insensitivity at 2.05 THz and the high-sensitivity of 504 GHz/RIU (RIU = refractive index unit). According to the frequency shifts and transmittance variations, four cell types are successfully distinguished from each other. The minimum number of cells is required for thousands of cells to display the differences of spectra, which is 1/30 of clinical methods. Furthermore, the results were consistent with pathological results (the gold standard in clinic) by Gaussian curve fitting. The proposed biosensor has really achieved the characterization of cells in normal and cancerous state. This detection strategy dramatically reduced the cost of detection by reuse and time consumption was reduced to 1/20 of the pathology testing. In addition, it is flexible to set samples and easy to realize automatic operation due to the great polarization-insensitivity of the proposed biosensor, which can further reduce labor costs in the future. It is envisioned that the proposed biosensor will present immense potential in the fields of cancer detection, distinguishing different cancers, and identifying primary lesion cancer or metastatic cancer.