Many children suffer from cancer relapses due to shortage of a drug that was used to treat cancer since the 1960s, a new study has found.

Researchers say that the replacement drug hasn't been effective in keeping children cancer-free for long. The study shows how a drug shortage can adversely affect people in a particular subgroup.

"This is a devastating example of how drug shortages affect patients and why these shortages must be prevented. Our results demonstrate that, for many chemotherapy drugs, there are no adequate substitute drugs available," said Monika Metzger, MD, an associate member of the St. Jude Department of Oncology and the study principal investigator.

Cyclophosphamide is used to treat Hodgkin lymphoma in both adults and children. Previous research has shown the drug to be effective and safe alternative to mechlorethamine - a drug which has been used in treating cancer since 1960s. Mechlorethamine shortage was reported in 2009.

Hodgkin lymphoma is a cancer that affects the lymph system and accounts for nearly 6 percent of childhood cancer.

After the drug mechlorethamine was replaced by cyclophosphamide due to drug shortages, cancer-free survival (for two years) for the study patients fell from 88 percent to 75 percent. Study patients who have relapsed require additional intensive therapy that can lead to health complications later in life.

"We can think of no credible explanation for this dramatic difference in event-free survival other than the drug substitution," the researchers noted.

Patients who received cyclophosphamide had an intermediate risk of Hodgkin lymphoma and also developed fewer unfavorable symptoms. The study patients were between 3 to 21 years of age, half of them were aged below 14.

Researchers say that the study provides proof of drug shortages causing real problems to the patients. They added that despite efforts by Food and Drug Administration to solve drug shortage problem, many patients still don't receive life-saving drugs.

The study is published in the New England Journal of Medicine and involves researchers from St. Jude Children's Research Hospital, Stanford University School of Medicine and Lucile Packard Children's Hospital at Stanford; Dana-Farber Cancer Institute and Boston Children's Hospital; Massachusetts General Hospital; and Maine Medical Center.