Apparatus and methods are described for use with a subject suffering from cancer. A nanoparticle (22) includes an inner core (30) that comprises a phase-change material that is configured to absorb latent heat of fusion by undergoing a phase change. An outer layer (32) disposed around the inner core includes a plurality of nano-spheres (34) of at least one metal, and a plurality of molecules (38) of a substance that binds preferentially with cancerous cells relative to non-cancerous cells. The nanoparticle has a volume of at least 65,000 nm3 and is elongatable into an ellipsoid, such that, when the nanoparticle is maximally elongated, each of the semi-axes defined by the ellipsoid is greater than 5 nm, and at least two of the semi axes of the ellipsoid are less than 30 nm. Other applications are also described.
