Constellations weren't "found" in a specific year. They were identified and named by ancient civilizations over thousands of years.

The constellation Cancer (the Crab) is one of the oldest known constellations. It is part of the zodiac, meaning it lies along the ecliptic path the sun appears to take across the sky.

Ancient Babylonian star catalogs from around 2000 BC already included Cancer, and it was also recognized by the ancient Greeks, Egyptians, and other cultures.