A focal ablation assembly, used with an endoscope comprising an endoscopic tube, comprises a cap and a cryogenic catheter placeable within the endoscopic tube channel. The cryogenic catheter defines a catheter lumen and has a distal end placeable at the endoscopic tube distal end. The cap is mountable to at least one of the distal ends and extends distally of both. The cap comprises a material which substantially maintains its shape during use while not causing tissue trauma. The cap defines a limited area therapeutic region, which is a chosen one of an open therapeutic region and a covered, effectively thermally transparent therapeutic region providing effectively no thermal insulation. In some examples the assembly includes a delivery catheter extending along the channel with a distal portion fluidly coupled to the cap volume, whereby refrigerant can be introduced into the cap volume and towards the therapeutic region by the delivery catheter.
