Cancer drug shortages are impacting the quality of care for a high number of patients, according to a new study presented at the 2013 annual meeting of the American Society of Clinical Oncology.

As the largest study of its kind to date, the report shows that shortages, which have hit drugs to treat pediatric, gastrointesntinal and blood cancers the hardest, are leaving doctors unable to prescribe standard chemotherapy.

In discovering this the research team surveyed a random sample of 500 board-certified U.S. oncologists in late 2012 and early 2013 in order to decipher the impact of drug shortages in their practice during the previous six months.

Of the 250 physicians who responded to the survey, 83 percent said they've faced a drug shortage.

Of that number, 78 percent said drug scarcity had forced them to treat a patient with a different drug or drug regimen while 77 percent said they had to substitute different drugs partway through therapy.

Furthermore, 43 percent said they were forced to delay their patients’ treatment and another 37 percent had to choose among patients who needed a particular drug.

Finally, 29 percent reported omitting doses, 20 percent reducing doses and 17 percent simply referred patients to another practice..

Dr. Keerthi Gogineni is an instructor in the division of Hematology-Oncology with the University of Pennsylvania's Abramson Cancer Center as well as the study’s lead senior author.

Of the study, she said in a press release, "Our results indicate that the vast majority of oncologists in the country are facing wrenching decisions about how to allocate lifesaving drugs when there aren't enough to go around."

And while much of the burden of decision-making may rest on oncologists, the potential effects on the patients include increased health risk as well as a general driving up of the costs of cancer care.

In a recent study, St. Jude's Research Hospital linked drug shortages to higher relapse rates among young people with Hodgkin lymphoma, with the number of patients who were cancer free after two years falling from 88 percent before the shortage to 75 percent after when doctors had to substitute an alternate drug.

However, despite the widespread nature and severity of the problem, the study’s authors further noted that 70 percent of doctors surveyed said their cancer centers or practices had no formal guidance in terms of allocating drugs.

"This is a dynamic problem, and when we learn about new shortages on the horizon, there is usually not a lot of time to plan for how to deal with them," Gogineni says. "Guidelines must be rapidly updated and disseminated, both to large academic medical centers and smaller community hospitals and practices -- where the majority of cancer care is delivered and which often lack the bulk-buying power to keep scarce drugs in necessary supply."