Simplify the following text for a Grade 11 native English-speaking person.
Original: Renal medullary carcinoma has been termed `` the seventh sickle cell nephropathy '' because it is found almost exclusively in individuals with sickle cell trait or occasionally in those with sickle cell disease .
Simplified: Renal medullary carcinoma is a rare form of Renal cancer that occurs most often in patients with Sickle cell trait or Sickle cell disease .