Cancri IV was the fourth planet in the Cancri system, 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.