Vaccine virus 'cancer link'

Early vaccines may have included monkey virus by mistake

A monkey virus found in early versions of a vaccine against polio may be linked to a common type of cancer, suggest scientists.

However, other experts are still doubtful whether the virus - or the vaccine - can be blamed.

Batches of polio vaccine tainted with "simian virus 40" (SV40) were given between 1955 and 1963.

This was because monkey kidney cells were used in the jab's production process.

Non Hodgkin's: Key facts

287,000 cases worldwide each year

Non-Hodgkin's in fact a collection of a dozen different cancers of the lymphatic system

Incidence increasing - perhaps partly due to ageing population

Causes not yet established

On average, between 50% and 70% survival after five years

Approximately 30m people may have been given the contaminated vaccine between these dates.

It has also been alleged that the virus which causes Aids was passed from primates to humans in this way, although close examination of frozen samples of 1950s batches appear to suggest otherwise.

However, it is conceded that SV40 was present in the early vaccine - and the latest research, published in the Lancet journal, has linked it to non-Hodgkin's lymphoma.

This is a cancer of the lymphatic system, which has a role in the body's fight against infection, and affects mainly the over 40s.

'Footprints' found

The researchers looked at hundreds of tumours taken from various cancer patients, and compared them with 68 samples taken from non-Hodgkin's patients.

They found genetic "footprints" of the virus in 43% of the non-Hodgkin's tumour cells.

Genetic traces of the virus were found

In other types of tumour, some had no trace of the virus at all, and fewer than 10% of most other types tested positive.

Tissue taken from 40 apparently healthy patients produced no positive tests at all.

Dr Ali Gazdar, from the University of Texas, who led the research, said the results confirmed earlier research on animals which linked the virus to brain and bone cancers, and uncommon types of lung cancer and lymphoma.

There has been no increase in these cancers which might have been expected if polio vaccine was the source

Professor Robin Weiss, University College London

The Lancet also printed the results of a separate experiment, carried out at the Baylor College of Medicine in Houston, which tested more than 150 non-Hodgkin's tumours.

Researchers found virtually identical results - 42% of the tumours had the SV40 "footprint", while 186 non-malignant control samples all tested negative.

Historical puzzle

Despite this evidence linking the virus to the cancer, there is still no proof that SV40 actually causes it in humans, although animal experiments suggest this can happen.

In addition, it is not proven that the polio vaccine was the source of the SV40.

Some patients born long after the contaminated batches were given have tested positive for the virus, yet scientists are unsure whether it is communicable between humans.

Professor Robin Weiss, from University College London, told BBC News Online it was possible that humans had actually given the virus to monkeys in the first place.

"I would challenge the idea that SV40 has come from monkeys - how do we know that?"

He said it might be the case that the virus was found in these particular cancer cells simply because they provided favourable conditions for it.

"We know that viruses like to grow in cancer cells, and this may be what is happening here.

"People go fishing around in tumours for SV40, but there has been no increase in these cancers which might have been expected if polio vaccine was the source."

Over the past decade, viruses and even certain bacterial infections have become far more accepted as contributory causes for particular types of cancer.

Human papillomavirus (HPV) is likely to play a significant role in the development of cervical cancer, and the bacteria H. pylori in the development of gastric cancers.