In my countys news, like an hour ago, they told us that even common objects like a pen are good to defend against an attacker with a knife, can you belive that? Good luck, lol. Can't make that shit up.
If all you have is a pen, it is better than bare-handed.
A pen has about the same cross-section as a knife. If you can grip it tight enough not to slip, it will stab just as deeply. Lack of a real handle makes gripping difficult, and of course there is no ability to slash. But the defensive mindset will be prepared to make use of any available tool.