This paper presents a new preclinical microwave hyperthermia system based on the combination among horn antenna and convex lenses. The horn antenna is designed to resonate at 3 GHz which is reported for hyperthermia therapy. Two convex lenses are designed and incorporated with the designed horn antenna and the reported breast phantom. The proposed system aims to heat up the tumor region above 42oC while keeping the surrounding area temperature unchanged as possible to protect them from damage. Specific Absorption Rate (SAR) and breast phantom thermal distribution are studied with and without using lenses at different inclination angles. The proposed system has the advantage of heating up different zones separately while keeping other regions temperature unchanged. Simulation results show that, the breast temperature can be elevated by 10o C above the normal body temperature.