Cancri IV was the fourth planet in the Cancri system. This planet was located somewhere in the Alpha or Beta Quadrant. The world was inhabited by the Cancri.
In 2256, the elders of Cancri IV hosted a secret meeting between Vulcan and two independent Klingon Great Houses to discuss the possibility of an alliance, with the planet serving as neutral ground.
However, the meeting was a ruse created by Kol originally in order to capture Ambassador Sarek, whom he had invited to the meeting. Due to a injury, though, Sarek did not attend the meeting, and Admiral Katrina Cornwell went in his place. Though Kol had wanted to capture a high-ranking Vulcan, he considered Cornwell an even greater prize. In the process, the Cancri hosts of the meeting and Cornwell's security escort were all killed. (DIS: "Lethe")
According to the revised Stellar Cartography: The Starfleet Reference Library ("History of the United Federation of Planets"), the Cancri system was located in the Beta Quadrant.