Many cancer patients are foregoing prescribed oral treatments because of high out-of-pocket costs, a new study led by University of Pennsylvania researchers suggests.

Using a national database of Medicare and private health insurance claims in 2014-15, the researchers looked at whether patients' unreimbursed expenses were a deterrent to filling prescriptions for 38 therapies given in pill form. Oral drugs are generally newer, molecularly targeted treatments and are more expensive than intravenous cancer drugs.

Overall, 18 percent of the 38,000 patients didn't fill an oral drug prescription after it was approved by their insurance. But cost was a big factor: Nearly half of those who were charged more than $2,000, and almost a third who owed $100 to $500, skipped their prescribed drug. In contrast, only 10 percent who were charged less than $10 did so.

The patients facing out-of-pocket costs over $2,000  — who made up 12 percent of the group — were also more likely to delay the start of oral therapies, and less likely to switch to an alternative pill or intravenous medication, according to the analysis published online this week in the Journal of Clinical Oncology.

Lead author Jalpa A. Doshi, a pharmaceutical policy researcher at Penn's Perelman School of Medicine, said she was surprised that so many patients gave up oral treatment, considering that cancer is a life-threatening disease.

"It's not a psoriasis patient. We are talking about cancer patients leaving their life-saving or life-prolonging medication at the pharmacy," she said.

Unless financial barriers are reduced, "patients aren't going to be able to access the true benefits of these new treatments," Doshi added.

While the problem is clear, the solutions are not, especially as employers continue to shift health insurance costs onto workers.

In recent years, Pennsylvania and 42 other states have passed "chemotherapy parity" laws intended to make oral drugs more affordable. Federal legislation is pending. The statutes — which only apply to fully insured health plans, not Medicare or self-funded private plans — require that oral drugs be covered  under "no less favorable" terms than intravenous chemotherapies.

Traditionally, insurance plans have covered IV chemo as a medical benefit because it requires going to a hospital or doctor's office for infusions; patients paid less than $50 per treatment. In contrast, pills have been covered as a pharmacy benefit, with the patient required to chip in as much as 25 percent of the price — even for new therapies that cost $100,000 or more for a treatment course.

A University of North Carolina study published in November that looked at out-of-pocket spending before and after the laws found they "modestly improved" what most patients had to pay. But for patients facing very high out-of-pocket spending, the costs actually went up.

Advocates insist the mandates have helped.

"Legislation aimed at leveling the playing field in terms of out-of-pocket costs between IV chemotherapy and oral treatments can help relieve the financial burden on patients, and help prevent treatment abandonment," said  Robin Levy, senior director of public policy for the International Myeloma Foundation, an organizer of the Patients Equal Access Coalition.

Doshi said the new study was not intended to assess the impact of parity laws, which existed in about 40 states by mid-2015. However, to make sure the laws did not bias the results, the analysis was repeated to adjust for whether patients lived in a state with or without a law. The bottom line was the same.

"We still found a similar relationship between increasing out-of-pocket costs and abandonment of oral medications," she said.