[eng] Most human pathologies are reflected in the blood content, in the form of so-called molecular biomarkers. These are biochemical species whose size is measured on the nanometric scale. Technological development on this scale is currently the subject of great research efforts. The field of nanosensors is one of the main exponents of these advances, which is allowing for increasingly precise estimates of the chemical concentration of any substance in a solution. However, despite these favorable circumstances, the use of nanosensors in the human circulatory system is a very little explored alternative. This paper aims to contribute to partially filling this gap. Specifically, we propose a system based on a swarm of nanorobots with integrated nanosensors, capable of monitoring the concentration of a specific biomarker to assess the presence of cancer. This assessment is performed by a temporarily implanted fusion center, which collects information from a subset of the activated nanorobots, which have detected the aforesaid biomarker, and then runs a decision algorithm based on a response-threshold method to assist in the diagnosis. In the future, the proposed system can become an effective and precise local chemotherapy tool if nanorobots are equipped with therapeutic capabilities. This would avoid the side effects of conventional cancer treatments.