Biomarkers can be assumed to indicate normal biological processes, pathogenic processes, or pharmacologic responses to therapy. In particular, cancer biomarkers (CBs) are specific proteins and/or oligonucleotides spread into body fluids during the early stages of cancer at abnormal levels concerning those found in healthy people. Moreover, they are important in providing data indicating the type and phase of the cancer and to monitor and evaluate treatment efficacy. Consequently, one of the best solutions for early cancer diagnosis is following CBs. Cancerous or noncancerous cells produce CBs in response to cancer or some specific conditions. Although CBs are generated in normal situations, their concentration is much higher in the presence of tumors. CBs are proteins already present in body fluids such as blood, serum, and urine. An increased level of CB may be due to cancer; however, it is not a definite indicator. For that reason, a combination of biomarkers and other diagnostic tests is always preferred. Due to the high cost, low speed, and intricate instrumental requirements of existing assays such as enzyme-linked immunosorbent assay and fluorescence and radiometric immunoassay for measurement of CBs, there is an extreme need for more inexpensive, swift, simple, and portable detection methods. Rapid progress in identifying biomarkers has increased the demand for high-performance detection technologies, and the use of biosensors has accelerated diagnostic activities. In recent years, the popularity of electrochemical biosensors has been increasing in diagnostic fields. In particular, the progress of electrochemical biosensors is probably an encouraging problem-solving approach related to sensitivity, velocity, and selectivity. Consequently, it is to be underlined that the implementation of electrochemical biosensors in tumor diagnosis can provide an effective answer to the growing need for rapid, specific, inexpensive, and fully automated devices of biomarker analysis. The advances from the past 5 years in the development of electrochemical sensors based on carbon nanotubes and carbon dots for CB determination are included in this chapter. In addition, the challenges and opportunities to integrate electrochemical sensing platforms into point-of-care solutions are discussed.