<p>This study explores the theoretical design of a one-dimensional ternary photonic crystal with parity-time (PT) symmetry for terahertz-based optical biosensing of oral cancer. The proposed structure follows the arrangement (<i>ABA</i>)^<i>N</i>/<i>D</i>/(<i>ABA</i>)^<i>N</i>, where layers A (doped SiO₂) and B (Si) form the periodic lattice, and D serves as a defect layer containing either healthy or cancerous oral cells. Transmission spectra were analyzed under varying PT-symmetry parameter (Q) conditions, revealing distinct defect modes within the photonic bandgap that exhibit strong dependence on the optical properties of the biological tissue. Comparative analysis between healthy and malignant cells showed notable variations in transmission amplitude and peak positions, with peak transmittance reaching 7.41 × 10¹⁰ at optimized Q-values. The system demonstrated exceptional sensitivity, achieving a maximum transmittance-based sensitivity of 2.1 × 10¹² %/RIU, highlighting its capability to detect minute refractive index changes. These results indicate that the PT-symmetric photonic crystal structure provides a highly sensitive, non-invasive, and label-free optical platform for early and precise oral cancer detection in the terahertz regime.</p>