Based on an investigation by NSW Health, pollution has been ruled out as the cause of a cluster of brain tumours reported in a Hunter Valley mining town.

According to a professor of public health at the University of Sydney, Bruce Armstrong, the five cases of brain tumours in a single block in Singleton were most likely due to chance.

Early this month, five residents in Singleton were reported as suffering from brain tumours, triggering fears of pollution from the coal mines and power plants of the region was behind the cause in the increased cancer rates in the town.

Two of the residents have died, while the third is on a drug treatment he hopes will extend his life by a few months. Two others have recovered.

The five people who resided in Singleton for 35 years or more had been diagnosed with three different types of brain tumours, which include two benign ones, from 1979 to 2008, according to the investigation.

Out of the five people who developed brain tumours, three had work associations with the coal industry.

Statistics obtained from the NSW Cancer Registry from 1979 to 2008 found the rates of malignant brain tumours in the Singleton area was not substantially different from the rate for all of NSW.

Prof Armstrong who examined the cancer cluster care at the ABC's Brisbane studios in 2007 said there was no particular environmental risk factor in the singleton area that might be associated with the brain tumour occurrence.

He believed there was a reasonable probability that such a geographical grouping could occur by chance and added that broader investigations may not really be beneficial.