(Reuters) — Worldwide spending on cancer medicines will exceed $150 billion by 2020, driven by the emergence of expensive new therapies that help the immune system attack tumors, according to a global oncology report released by IMS Health Holdings Inc. on Thursday.

That represents an annual global growth rate for oncology drug spending of 7.5% to 10.5% through 2020, up from last year's IMS forecast of 6% to 8% growth through 2018.

The figures are based on the medicines' list prices, which exclude discounts and rebates, and also include supportive care drugs to address side effects like nausea and anemia associated with many treatments, particularly chemotherapies.

Global oncology drug spending reached $107 billion in 2015, an 11.5% increase over the prior year and up from $90 billion in 2011, as some 70 new cancer treatments for more than 20 tumor types entered the market over the past five years, IMS found.

"The new science redefining cancer as a large number of narrowly defined diseases and yielding therapeutic options for an expanding number of patients is rapidly transforming the oncology treatment landscape," Murray Aitken, executive director of the IMS Institute for Healthcare Informatics, which produced the report, said in a statement.

However, more than half of those new drugs are available to patients in only six countries, and even fewer are reimbursed under public insurance programs, the report said.

The report was released just ahead of the American Society of Clinical Oncology meeting in Chicago, the year's most important scientific cancer meeting.

The transformed landscape has been shaped by a wave of new drugs that enable patients' own immune systems to better attack cancer, leading to unprecedented survival rates for some of the most deadly diseases, such as advanced melanoma and advanced lung cancer.

Bristol-Myers Squibb Co. and Merck & Co. Inc. have been leaders in the field, while Roche Holding A.G. last week won U.S. approval for an immunotherapy that became the first new treatment for advanced bladder cancer in 30 years. Many more immunotherapies and other types of new cancer treatments from companies large and small are on the way.

IMS, which provides prescription drug use data for the pharmaceutical industry, said it found 586 cancer treatments from 511 companies were in mid- to late-stage development.