Today, cancer disease is a significant reason for the death of many patients. In many cases, cancer is diagnosed after metastasized during the body. Thus, the earlier detection gives a better opportunity for treatment and cure. A simple 1-D binary photonic crystal with a defect layer is proposed with the structure (Si/ SiO2)N/Defect/(Si/ SiO2)N as a detector for cancerous cells. The defect layer is taken here as the patient's blood sample. Compared with the normal blood sample, the cancerous samples lead to a considerable change in the refractive index. This index variation leads to a shift in the resonant mode position which can be used to diagnose cancer cells. The transfer matrix method is employed to analyze the structure. The number of periods, defect layer thickness and incident angle are investigated to maximize the sensitivity. The sensitivity is calculated at optimized conditions and found as 2400.08 nm/RIU. This sensitivity is extremely high when compared to the most recent biosensors. All the sensor performance parameters are calculated and discussed.