The new study, Lu-Yao said, reaches even more persuasive conclusions because it followed more than 66,000 patients for 17 years.
Experts in the field have not endorsed hormone therapy, known as ADT, as the main treatment in patients in which cancer cells have not spread.
"Nevertheless, it was used quite commonly," said Lu-Yao, an epidemiologist at the Cancer Institute of New Jersey and professor of medicine at Rutgers Robert Wood Johnson Medical School.
The estimated costs to Medicare for men who received the unnecessary hormone treatment is about $42 million, according to the paper.
Aside from the costs, there are potentially serious health consequences.
"It really is not a benign treatment," said Alan J. Wein, professor and chief of urology at the University of Pennsylvania.
"Androgen-deprivation therapy is palliative, not curative," Wein explained. For patients with advanced disease, it can be very effective in relieving symptoms and shrinking the cancer.
"But ADT also has been associated with thinning of the bones, weight gain, decreased muscle tone, the appearance of diabetes, and perhaps deep venous thrombosis," Wein said.
Few specialists in academic medicine will be surprised at the findings that hormone therapy alone does not prolong life in low-risk patients, Wein said.
"What is surprising is that they were able to collect so many patients," he said.
The study, which followed patients from 1992 to 2009, covered a cross-section of the United States, including parts of California, Hawaii, and New Jersey, but not Philadelphia.
In the rapidly evolving world of medicine, Wein said, five years is a significant period.
"I would suspect that among the more contemporary-trained people who completed their residency in the last five years," Wein said, "there is far less use of ADT in patients who have localized cancer."
The other paper published Monday, by a team from MD Anderson Cancer Center in Houston, found that within the first 12 months of treatment, prostate cancer patients tend to receive the type of therapy that coincides with their doctor's specialty.
The most appropriate treatment for patients with slow-growing, localized disease, experts say, is usually "active surveillance," in which patients regularly see a physician to make sure that no cancer cells have spread. But who received that care varied widely.
"If you saw only a urologist, you were more apt to be placed on active surveillance than if you were also seen by a radiation oncologist," said Wein.
The study found that 43.8 percent of low-risk patients who solely consulted a urologist were monitored carefully, going for regular checkups to see if their cancer was progressing.
By contrast, only 8.6 percent of patients who saw a radiation oncologist as well as a urologist left the office without a plan to receive some sort of treatment or procedure.
"That's an incredible difference," said Wein, who was not involved with either of the new studies.
The reasons for the discrepancy, several experts said, are purely speculative.
Clearly, however, part of the push for treatment comes from patients.
"Often men will feel they want to do something. It's difficult to just wait and observe," said Tom Kirk, president and CEO of Us TOO, a prostate cancer support organization.
"What these studies do is reinforce what we tell people: Don't just take the advice of one doctor. You wouldn't take your Chevy to a Ford dealer, so if you think radiation is best for you, you need to talk to a radiologist. But you have to get second opinions and talk to other specialists, too," Kirk said.
Although there is nothing groundbreaking in the new papers, they serve as a reminder that both medical professionals and patients need to be better educated, said David Chen, associate professor of surgical oncology at Fox Chase Cancer Center.
Doctors, who make a living providing care, are naturally inclined to offer treatment, he said - and patients, who are naturally frightened by any cancer diagnosis, want to be treated.
"There are," Chen said, "a number of conscious and subconscious pressures."
When Wein offers "active surveillance" to patients with localized disease, especially those who are over age 60, he said he describes the option as a gamble.
"If you win the bet, and the cancer does not progress, you've lost nothing," he explained. "If you lose the bet - and most people don't lose the bet - you haven't really lost."
The patient may turn out to need radiation, surgery, or other intervention, Wein said. "But statistically, they're no less curable than if they'd had treatment at the outset."