KLK3 and neoplasm: Table 4 summarizes their analytical performance in liquid biopsy applications. Having established the core characteristics of photonic biosensing platforms for the main circulating biomarkers, the subsequent sections focus on clinically relevant tumor biomarkers: HER2, CEA, and PSA. As detailed in Section 2, these were selected due to the high incidence and clinical importance of prostate, breast, and lung cancers, which can be detected at early stages through these markers.