If you have a Tumor familiar attached to your back looking backwards your level high enough to have speak with your master, would this negate flank like all around sight because your familiar can warn you of the dangers behind you? LOL Just wondering.
BUT! If you really want it to help mitigate flanking, make it a Valet familiar (it automatically shares all teamwork feats the master has) and take the teamwork feat Back to Back. Gives you both +2 to AC when flanked :)