Women in the north of England are far less likely to survive breast cancer than those living in the wealthy South-east, according to a major new study which exposes a postcode lottery in treatment of the disease.

In the worst areas, just 66 per cent of women will still be alive five years after breast cancer is diagnosed. That rises to 85 per cent where treatment is most effective.

Survival rates are generally lowest in the poorest areas of the country, and one theory is that poorer people may get poorer treatment.

"The potentially explosive question is, do these people receive less effective treatment than rich people?" said Professor Michel Coleman of the London School of Hygiene and Tropical Medicine, who led the study. "We know that women who are treated by specialist surgeons have better outcomes, and we have evidence from Scotland and Yorkshire that poor people tend to see a specialist in their particular disease less often than rich people.''

In the research, reported in the British Journal of Cancer, data on almost 80,000 women diagnosed with breast cancer was examined by health authority area. Of the 78,904 women included, 27,532 died within five years of diagnosis, and the average five-year survival rate was 75 per cent.

"There is evidence of geographical similarities among the northern regions, with the relative survival rates in North-west, Trent and Northern and Yorkshire being on average considerably lower than in London and in the Eastern and South-east regions,'' says the report.

The researchers say that the differences are unlikely to be down to chance or differences in the extent of disease at the time of diagnosis.

"For breast cancer patients, these differentials have been associated with variations in diagnostic investigations both in England and Wales and in Scotland, and with departures from treatment guidelines,'' says the report.

The researchers found that health authorities with higher numbers of lower social class households, or higher unemployment rates, or greater deprivation, had lower breast cancer survival rates.

"It could be that poorer people have immune systems that are not so good as wealthier people, or it could be their nutritional status is not so good," said Professor Coleman. "It could also be that the state of diagnosis is more advanced.

"The only other explanations are related to the health-care system: do poorer people get diagnosed less effectively, investigated less thoroughly, or treated less comprehensively? It is quite probable that all of these play a part."