A mains electricity (AC-powered) device assembly designed for controlled heating (i.e., temperatures above 43° Celsius) of the body using microwaves, for the treatment of malignant or benign tumours or other disease conditions [e.g., benign prostatic hyperplasia (BPH), prostatitis]. It includes a microwave generator, controls, software (e.g., treatment planning software) and a microwave applicator. It is intended for both whole-body and localized heating of tissues/organs through either externally-mounted components or from catheter- or probe-type applicators inserted topically, endoscopically, or surgically.