A Helston couple whose 19-year-old daughter died from bone cancer have condemned an investigation which concluded there was no link between a suspected cluster of cases of the disease in and around the town.

Health experts who have been looking into cases of osteosarcoma in young people in the Helston area said the higher than expected number of cases over the last five years was a "chance rise" and not a cause for public concern.

But Gill and Richard Callar, whose daughter Emma died from the rare bone cancer last August, branded the investigation a "whitewash".

"We would have waited a year or two if we felt they were doing it properly, but they have not," said Mrs Callar. "They have just skimmed over everything rather than looking into it properly. We were only asked four questions. How can you find out from four questions whether these children are linked? There is nothing new in this report. It is just a whitewash."

The couple, who led calls for a probe into the suspected cluster, say they will continue to pressure the authorities in a bid to secure a "proper" investigation.

Mr Callar said: "It is not that we want them to find a link. We don't want anyone else to have to go through what we've been through. We just want to feel they have looked at everything and we don't think they have done that yet."

The couple were among those attending a briefing on the findings of the investigation at the Guildhall in Helston yesterday afternoon. Also present were the family of Helston teenager Aimee Plant, who is suffering from osteosarcoma.

Dr Julia Verne, director of the South West Cancer Intelligence Service, which carried out the investigation, told the meeting there had been four cases of the bone cancer in west Cornwall between 1998 and 2002. Of those four cancer sufferers, three attended Helston School and Community College although only two lived in the immediate area.

Looking at the figures, it was "highly unlikely" there were common environmental factors linking the cases. Dr Verne said: "There is no evidence of a worryingly high level of cases of osteosarcoma in the west of Cornwall. I understand that people may feel that four cases in five years is a high rate for a rare cancer, but short-term increases in rates of specific cancers is not uncommon."

Dr Verne was keen to allay families' fears they could have done something to prevent their children from developing the disease.

"There is nothing that could have been done and nothing that we ought to be doing to protect children against developing osteosarcoma in this area," she said.

The probe was launched following a request from Dr David Miles, director of public health for the West Cornwall Primary Care Trust.

In a statement issued yesterday, the PCT said: "The trust is pleased that the South West Cancer Intelligence Service has been able to conduct this investigation in response to our request for expert advice.

"The review has been carried out with great care and sensitivity and we welcome the findings, which we believe will reassure local people