A system configured for photodynamic or photothermal therapy and photodynamic diagnosis of a tissue is 5 disclosed. The system comprises in combination an assembly of: a proximal end adapter for a catheter comprising an adapter body (32), having proximal and distal ends, defining an axial lumen extending between the proximal and distal ends, a catheter mounting element at the distal end 10 of the adapter body (32) for sealingly mounting a catheter to the adapter body, and a hollow catheter (31), wherein the catheter mounting element connects a catheter body to the hollow catheter so that the hollow catheter extends from the distal end of the catheter body； a first light 15 guide (36) having proximal and distal ends, wherein said first light guide is sealingly contained in said axial lumen defining an axial optical path extending between the proximal and distal ends of the adapter body (32) towards said tissue (8) and into close proximity thereof or 20 interstitially into said tissue； an optical connector mounting element at the proximal end having mounted an optical connector (37) to the adapter body, and wherein said optical connector (37) is coupled o to a light source via a second light guide (38), such that light from said 25 light source is transmittable from said light source via said second light guide (38) and further via said optical connector (37) to said first light guide (36) via said proximal end adapter towards said tissue (8) through said catheter (31).
