Needs review
Source: Epic Level Handbook

Description: You can cast a touch spell as an attack of opportunity.

Prerequisites: Epic Level, Combat Casting, Quicken Spell, Combat Reflexes, Spellcraft (25 ranks)

Whenever you are allowed an attack of opportunity, you may cast (and attack with) a touch spell as your attack of opportunity. This incurs attacks of opportunity just as if you had cast the spell normally.

Normal

Without this feat, you can only make a melee attack as an attack of opportunity