Possible Clues:

• Matter of debate
• Subject (of a text)
• Fuel for a debate
• Discussion theme
• The subject of coming first, I see
• Subject of work penned by Mark but remaining unfinished
• Cancer? There's no right to make it a talking point
• Item on a 9-Down
• Matter of a large circle getting a reduction in radius
• The head, I see, for the headline