Ronnie Hillman, a former Denver Broncos running back who helped the team win Super Bowl 50, died Wednesday, December 21, of a rare cancer that mostly affects young African Americans who also have sickle cell trait. He was 31.

In August, his family posted a statement on Instagram, sharing that he had been diagnosed with renal medullary carcinoma (RMC), a kidney cancer, and was receiving hospice care.

On December 21, they posted an update: “It is with heavy hearts that we announce the passing of our beloved son, brother & father, Ronnie K Hillman Jr.,” the statement read.

“Ronnie quietly and peacefully transitioned today in the company of his family and close friends,” the post continued. “We as the family, appreciate the prayers and kind words that have already been expressed. We ask that you would give us time to process our feelings as we prepare to lay our precious RJ to rest. More information will be forthcoming.”

RMC is a rare and aggressive cancer that affects the kidneys, according to the National Library of Medicine. It usually presents when it’s in a later stage and mostly among adolescents and young adults who have sickle cell trait. Prognosis is “extremely poor, with a mean survival of less than a year in most cases.”

Having sickle cell trait means that a person has one gene for sickle cell disease and one normal gene (inherited traits are created by two genes, one from the father and one from the mother). Having the trait does not mean you have the resulting disease. According to Cancer Health’s sister publication Real Health, a magazine for African American wellness, about 1 in 13 Black babies born in the United States have the trait.

When people have the disease, it is called sickle cell anemia. As the Real Health Basic on Sickle Cell Anemia writes:

Sickle cell anemia is an inherited form of anemia—a condition in which the body doesn’t produce enough healthy red blood cells or hemoglobin, a protein in red blood cells that carries oxygen through the body. Healthy red blood cells are round and flexible, but those of someone with sickle cell anemia are rigid and sticky and shaped like crescent moons. This irregular shape causes the cells to get stuck in small blood vessels, and it slows or blocks the flow of blood and oxygen to the body, resulting in numerous problems. For most people, there’s no cure for sickle cell anemia. But the condition can be managed with pain-relieving treatments that also work to help prevent further problems associated with the condition.

It was not reported whether Hillman had sickle cell trait.

“We are deeply saddened by the untimely passing of former Denver Broncos running back Ronnie Hillman,” the Denver Broncos said in a statement. “A key contributor during the winningest four-year period in franchise history, Ronnie was part of two Super Bowl teams and led the Broncos in rushing during our Super Bowl 50 championship season. Soft-spoken with a warm smile and quiet intensity, Ronnie was drafted by the Broncos in 2012 and grew into a dynamic player and well-respected teammate. Ronnie will be fondly remembered by our organization, which extends its heartfelt sympathies and condolences to the Hillman family during this difficult time.”

Hillman grew up in Long Beach, California, noted He became serious about a pro football career after participating in rapper Snoop Dogg’s youth football league and then playing college football for San Diego State.

In related football and cancer news, see “NFL Legend Terry Bradshaw Announces Cancer Diagnoses on Air” and “22 NFL Players Raise Cancer Screening Awareness Through “Crucial Catch.”