In this study, early cancer detection of a single living cell is investigated by employing a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) biosensor structure. The full-vectorial finite element method (FV-FEM) with perfectly matched layers are engaged for numerical analysis. The spectral interrogation and amplitude methods are used to detect the refractive index (RI) variations of cancer cells. The refractive index (RI) varied from 1.392 to 1.401 for six different types of cancerous cells. Obtained numerical results have indicated that, the highest sensitivities for spectral interrogation and amplitude methods are reported as 7142.86 nm / RIU for MCF-7, and \(-757 RIU^{- 1}\) for Hela cell, respectively.