Microwave ablation instrument with insertion probe

A microwave ablation assembly and method including a relatively thin, elongated probe (21) having a proximal access end (22) and an opposite distal penetration end (23) adapted to penetrate into bio-tissue (25). The probe (21) defines an insert passage (26) extending therethrough from the access end (22) to the penetration end (23) thereof. An ablation catheter includes a coaxial transmission line (28) with an antenna device (30) coupled to a distal end of the transmission line (28) for generating an electric field sufficiently strong to cause tissue ablation. The coaxial transmission line (28) includes an inner conductor (31) and an outer conductor (32) separated by a dielectric material medium (33). A proximal end of the transmission line (28) is coupled to a microwave energy source. The antenna device (30) and the transmission line (28) each have a transverse cross-sectional dimension adapted for sliding receipt through the insert passage (26) while the elongated probe (21) is positioned in the bio-tissue (25). Such sliding advancement continues until the antenna device (30) is moved to a position beyond the penetration end (23) and further into direct contact with the bio-tissue (25).