The two brightest stars in the constellation Cancer are:

* β Cancri (Beta Cancri): Also known as Altarf, it's a giant star with an apparent magnitude of 3.53.

* α Cancri (Alpha Cancri): Also known as Acubens, it's a binary star system with a combined apparent magnitude of 4.26.

While both are relatively faint compared to other bright stars in the sky, they are the brightest within the Cancer constellation.