While serving time in a Wisconsin prison in 2021, Darnell Price watched a golf-ball-size lump on his thigh grow as large as a football. Mr. Price pressed for a thorough examination, he said, but the prison’s physician, Dr. Joan Hannula, did not order a biopsy.

Months later, when Mr. Price moved to another prison, a different doctor ordered the test and diagnosed him with Stage 4 soft-tissue cancer. Soon after, the state’s Department of Corrections took the extraordinary step of granting him compassionate release, a measure reserved for the terminally ill or elderly.

“I did my time,” said Mr. Price, 52, who had been convicted of robbery of a financial institution. “But they took the rest of my life.”

Mr. Price filed a federal lawsuit against Dr. Hannula and four other medical employees this year. It is not the first time Dr. Hannula has come under scrutiny: Records show she surrendered her medical license in California in 2004, then pleaded guilty to a drug possession charge and no contest to a charge of forging a prescription.

In Wisconsin, where the arrests of multiple prison officials last month raised urgent questions about inmate care, Dr. Hannula is not an anomaly, an examination by The New York Times and Wisconsin Watch found. Nearly a third of the 60 staff physicians the state corrections system has employed over the past decade have been censured by a state medical board for an error or a breach of ethics, an unusually high concentration given how rare it is for a doctor to be formally reprimanded.

Almost all those censured staff physicians were disciplined before they began working in the state’s prisons.