Dr. Hudson was 33 and had just taken a position as head of urology at the Francis Delafield Hospital, a public cancer hospital in New York, when he and his colleagues began recruiting homeless men in 1951. He got the idea of going to the Bowery when he was caring for a man who had been a Princeton history professor but ended up a homeless alcoholic living there.

At first, Dr. Hudson said, the Bowery men resisted his offers. He recalled speaking at one of the flophouses just before bedtime. “I had a lot of old vegetables thrown at me,” he said. “I was talking about making a small incision in a very interesting part of their anatomy.” But many eventually agreed to participate.

Unlike modern prostate biopsies, which involve the use of a thin needle, the biopsies done in the Bowery study involved cutting a small slice out of the men’s prostates. Dr. Hudson said he told the men they might get a local infection from the biopsy, but a man who worked as a urology resident on the project told Dr. Aronowitz that he saw many other complications in the Bowery men.

Dr. Aronowitz got the approval of his university’s ethics committee to speak to the former resident, who had just read “The Immortal Life of Henrietta Lacks,” the best-selling book about a black woman whose cancer cells were cultured without her permission in 1951.

Worried about the ethics of the Bowery study, the former resident declined to be named in the paper, but told Dr. Aronowitz in a recorded interview that the biggest fear among the doctors doing the biopsies was that they would cause rectal perforations, and he regretted not telling the men in writing about that risk.

Aware of Dr. Hudson’s contention that the biopsy would not cause serious injuries, two urologists published case reports in 1957 on the experiences of 24 men who had biopsies that found no cancer. Many of them had serious complications, including rectal lacerations. A third of them became impotent and another third had diminished sexual function.