(Reuters) - The cost of treating cancer in the United States will rise 27 percent to at least $158 billion by 2020, assuming treatment costs and survival rates remain stable, U.S. government researchers said Wednesday.

If new diagnostic tests and cancer treatments continue to grow more costly, it could cost $207 billion a year to treat cancer in the United States, researchers from the National Cancer Institute report in the Journal of the National Cancer Institute.

They said even though overall rates of new cancer diagnoses are slowing in the general population, the number of people diagnosed with cancer will keep rising as the number of elderly Americans jumps from 40 million in 2009 to 70 million in 2030.

Here are some projections about the cOst of treating cancer in the United States in the next decade:

* Using data from a 2005 national database, the team estimated medical costs associated with cancer were $127*6 billion in 2010.

* Assuming stable costs and survival rates, cancer costs will reach $158 billion in 2020.

* If the costs of cancer diagnostic tests and treatments rise 2 percent per year, the cost of treating cancer could rise to $173 billion by 2020.

* If treatment costs rise 5 percent per year, treating cancer in the United States could jump to $207 billion a year.

* In 2010, breast cancer was the most costly to treat at an estimated $16.5 billion, followed by colorectal cancer at $14 billion, lymphoma at $12 billion, lung cancer at $12 billion and prostate cancer at $12 billion.

* If cancer incidence and survival rates remain stable, the number of cancer survivors in 2020 will increase by 31 percent to about 18.1 million.

* Because of the aging of the U.S. population, the largest increase in cancer survivors over the next 10 years will be among Americans age 65 and older.

Source: The Journal of the National Cancer Institute and the National Institutes of Health (Reporting by Julie Steenhuysen in Chicago; Editing by Vick