Prices of oral cancer drugs in the United States have risen sharply since 2000, a new study finds.

The average cost of a new oral cancer drug introduced in 2000 was about $1,869 a month, compared with $11,325 a month for one approved in 2014, about six times higher, United Press International reported.

Gleevec had one of the largest price increases during that time, rising about 7.5 percent a year and increasing from $3,346 to $8,479 a month, according to the University of North Carolina researchers.

The study was published in the journal JAMA Oncology.

The researchers said the skyrocketing prices have occurred along with health insurance changes making patients bear more of the cost, and potentially making treatment unaffordable for some, UPI reported.