Not quite sure what .cas files are, and why they are on my computer.

[Ethan_1701]

So pretty much I was trying to figure out why my hard drive was so full and I came across this file type using WinDirStat. Its called .cas and its represented in this picture in dark blue. I'm concerned because It takes up a really big chunk of my hard drive and I couldn't really find any info about it on the internet just by searching for it. I would appreciate if you could tell me what this could be.
Thanks

 

[stdragon]

Which directory are they listed in?

 

[thx1138v2]

What is .cas file?