A method of this invention for treating body tissues containing cancerous cells or non-malignant tumors with RF ablation, alone or in combination with systemic or localized chemotherapy comprising introducing a stylet comprising an electrode surface and a sleeve longitudinally moveable thereon into the vicinity of the body tissues, retracting the sleeve from a portion of the electrode surface, and supplying RF power to the electrode surface sufficient to heat the tissue to a temperature of above about 45.degree. C. for a time to cause reduction of tissue mass in the vicinity of the electrode. The RF power supplied to the electrode surface is sufficient to effect a desiccated fluid diffusion barrier capsule surrounding the body tissue being treated. The stylet can include a hollow tube having fluid distribution ports therein, and the method can include the step of passing fluid through one or more distribution ports into the body tissue being treated. The fluid can be saline or a chemotherapeutic fluid such as liquid or gas containing a cytotoxic agent, for example. The fluid can be administered in a variety of procedures. The fluid can be passed through a distribution port into the body tissue before, during and/or after the RF power is supplied to the electrode surface, for example. Preferably, the fluid is introduced after a barrier capsule has been formed. The devices comprises electrodes having a hollow core and a closed sharpened distal tip. The electrode has a plurality of fluid distribution ports therein for distribution of fluid treatment agents into the tissue.