Cassiopeia Runes explained
There's one set of runes for Cassiopeia on patch 14.9 that is the clear favorite for LoL players and pros alike. The best Cassiopeia rune paths on the position 
Mid are 
Precision as the primary path and 
Sorcery as the secondary path with a pick rate of 78%. Besides picking runes on Cassiopeia you should learn how to play Cassiopeia and if you are interested in pro matches take a look on how a pro builds Cassiopeia. If you want to discuss 
Cassiopeia then you should visit the champion subreddit.
Cassiopeia runes from primary path
Precision improves attack and sustained damage on Cassiopeia troughout the match. Most of high elo players – and our LoL pros in the the major regions – have agreed that 
Conqueror is the best keystone rune to run on Cassiopeia. This keystone rune provides additional power in the later stages of a game. As soon as Conqueror is fully charged, Cassiopeia deals additional damage and gains life steal. Other primary runes on Cassiopeia are 
Presence of Mind, 
Legend: Tenacity and 
Last Stand.
Presence of Mind helps Cassiopeia with the mana problems by restoring missing mana, if a champion is killed. Cassiopeia gains extra Tenacity with every additional stage of Legend: Tenacity. With Last Stand you deal more damage while you are at low health.
Cassiopeia runes from secondary path
When it comes to your secondary path, most Cassiopeia players prefer to go with Sorcery. Sorcery empoweres abilities of Cassiopeia and increases the available champion resources. On the Sorcery path, the best runes for Cassiopeia are 
Manaflow Band and 
Transcendence.
This is usually followed up by taking Manaflow Band for additional mana and mana regenaration. Transcendence for some more Ability Haste.
FAQ for Cassiopeia Runes
Which is the best keystone rune on Cassiopeia?
The best keystone rune on Cassiopeia is Conqueror. This Cassiopeia runes setup is then referred as Cassiopeia Conqueror.
What runes does Cassiopeia use?
Runes from the paths Precision and Sorcery are the most used runes on Cassiopeia. For the exact pick rates of Cassiopeia runes used, you have to study the rune distribution presented.