An apparatus and method for treating epithelial hyperproliferative diseases by application of an active composition over the diseased irregular tissue which is in the form of a viscous gel to carry the photosensitizer. The gel's viscosity allows it to adhere to the tissue for a sufficient time to transfer the photosensitizer or for a mechanical device such an expanding balloon to press the gel into the tissue. The photosensitizer within the gel is activated by the corresponding wavelenght of radiation. An extended multi-ballon system limits the area of treatment and localizes the spread of the gel. The apparatus, designed to be used with an endoscope, contains a catheter with at least two balloons, one to block drainage of the gel and one to limit the height of the treatment area and to press the gelinto the tissue.