Many optical and electrochemical sensing technologies as those described in Chapters 1.2 and 1.3 have been engineered to detect cancer biomarkers with both high affinity and high specificity. For such technologies to fulfill their potential and impact the way cancer patients are diagnosed and monitored, it is essential to incorporate them into functional devices that satisfy specific requirements. Device specifications are typically dictated by clinical requirements (what levels of specificity and sensitivity are acceptable) and by the intended end user's needs (e.g., research tool vs point-of-care test). In this chapter, we present general principles for designing cancer biosensors, focusing primarily on the recent advances in nucleic acid and protein sensors, whether their intended use is in well-resourced research facilities on at the point care (e.g., in a GP's clinic or on the field). The second part of this chapter focuses on the description of the most promising and most commonly used platforms, including microfluidic chips and lateral flow paper diagnostics. Finally, a selected number of successful case studies are presented that highlights how technologies developed and validated by bioengineers are improving the ways cancer is detected and treated.