All six cases are thought to have links with Helston Community College

The cases had been diagnosed at different times over the last five years, and not within a short time span, said a spokesman for the West of Cornwall Primary Care Trust.

Experts from the South West Cancer Intelligence Service (SWCIS) in Bristol have been called in following concerns expressed by local people about the number of cases.

They will try to determine whether there was any cause other than chance, said the trust spokesman.

The investigation will be conducted with great care Dr Julia Verne, South West Cancer Intelligence Service

All six cases are thought to have links with Helston Community College.

One former pupil, 19-year-old Emma Callar, first became ill in 1999 and died last month.

Another teenager, 15-year-old Amiee Plant, was diagnosed with bone cancer earlier this year.

She recently had an operation to remove her right leg.

Bone cancer is most common in adolescence, when the bones are growing fastest, and the cause of most cases is unknown, although a small minority may have a genetic link.

According to the children's cancer unit in Bristol, over the last 27 years the number of cases of bone cancer have been exactly as expected.

However, there have been more cases over the last five years than expected, said the trust.

Detailed analysis

The review by SWCIS would involve a detailed analysis of the cases, and would take some time, it said.

The acting director of the SWCIS, Dr Julia Verne, said the investigation was being undertaken in collaboration with the trust's public health team, doctors at the Royal Cornwall Hospitals Trust and the Children's Hospital in Bristol.

"In view of the concerns of the relatives and children, the investigation will be conducted with great care, and will involve detailed analysis of the cases.