THURSDAY, Oct. 6, 2016 (HealthDay News) -- Many older cancer drugs took a bigger bite out of Medicare and older Americans' wallets last year than five years earlier, a new analysis finds.

After adjusting for inflation, nearly two-thirds of 86 cancer medicines in the study had price increases between 2010 and 2015, researchers reported.

Eleven drugs more than doubled in price, and older drugs increased more than newer drugs, the study found.

The study included oral and intravenous chemotherapy drugs covered by Medicare Part B. Medicare is the federal health insurance plan for people 65 or older.

"Higher costs lead to higher copays," said study co-author Dr. Sham Mailankody. He's a medical oncologist at Memorial Sloan Kettering Cancer Center in New York City.

"And empiric research suggests higher copays lead to treatment delays or discontinuation," he added.

Patients with Medicare Part B coverage are responsible for up to 20 percent of the cost of these medicines.

Stacie Dusetzina, assistant professor of pharmacy and public health at the University of North Carolina at Chapel Hill, finds the price increases concerning.

"Patients who don't have a supplemental health insurance plan to help them with out-of-pocket costs will pay more as the price goes up," she said.

About 19 percent of Medicare enrollees lack that coverage, noted Dusetzina, who was not involved with the study.

When researchers split cancer drugs into two groups by their date of approval, older medicines jumped nearly 23 percent in price. That compared with a 6 percent bump for newer treatments.

"Raising the price of older drugs seems particularly objectionable when one considers that the outlay for research and development occurred long ago, and has almost certainly already been recouped," the study authors wrote.

Moreover, drug prices were unrelated to the drugs' benefits, they said.

The findings were published online Oct. 6 in JAMA Oncology.

Public scrutiny of older drug prices has intensified in the wake of recent dramatic price hikes.

Former Turing Pharmaceuticals CEO Martin Shkreli faced price-gouging accusations after bumping the price of Daraprim (pyrimethamine), an HIV and cancer drug, by more than 5,000 percent -- from $13.50 to $750 a pill.