Precision of flow sensing by self-communicating cells*

Metastatic cancer cells have been observed to detect the direction of lymphatic flow by “self-communication”: they secrete a chemical which, due to the flow, does not return to the cell surface isotropically. The secretion rate is low, meaning detection noise may play an important role, but the sensory precision of this mechanism has not been explored. Here we derive the precision of flow sensing for two ubiquitous mechanisms: absorption of the chemical and binding/unbinding to surface receptors. We find that the latter mechanism is significantly more precise due to the fact that absorption distorts the signal that the cell aims to detect. Comparing to experiments, our results suggest that the cancer cells operate remarkably close to the physical detection limit. Furthermore, we predict that they should bind the chemical reversibly, not absorb it, a prediction that is supported by endocytosis data for these cells.