Abstract: An implantable hypothermia instrument for the in-situ treatment of oncological disorders includes a cylindrical casing terminating at a first end in a concave tumor-abutting portion of a thermoconductive material which is thermally adjacent the cold junction of a cascaded three-component solid state cooler and shaped to partially surround the target tissue in order to provide a convergent freezing effect. The cooler comprises a thermoelectric first cooling section, a thermomagnetic second cooling section and an Ettingshausen third cooling section connected thermally in parallel to afford a stepped temperature reduction across a wide thermal gradient and to provide a temperature level, freezing rate and repetitive freeze/thaw cycles sufficient for tumor necrosis.