Key Points:

One of the most vilified pieces of medical research in New Zealand - gynaecologist Dr Herbert Green's "unfortunate experiment" - has given the world its most valid estimates yet of the risk of the precursor lesions known as carcinoma in situ, developing into cervical cancer.

A team of medical experts has extensively analysed the data compiled by Dr Green to confirm a high risk of cervical cancer in women not treated after finding precursor lesions - and a very low risk in women who received conventional treatment.

This is the opposite of the hypothesis tested by Dr Green when he received permission from senior medical staff at National Women's Hospital in Auckland in 1965 to verify that the lesions - known as cervical intraepithelial neoplasia 3 (CIN3) - were not a precursor of invasive cancer of the cervix.

From 1965, the hospital allowed treatment for some women with CIN3 to be withheld or delayed.

A team led by Dr Margaret McCredie, of Otago University, has now analysed the records of 1229 women - whose treatment was reviewed after a judicial inquiry in 1988 - and found that women who had minimal disturbance of their lesion with a punch or a wedge biopsy, had a 31 per cent risk of developing cancer over 30 years.

Women from the study who were adequately treated, commonly by means of a cone biopsy, faced a risk of less than 1 per cent over the same period. The retrospective study published early online in the Lancet Oncology web pages, involved researchers examining the medical records of the women in the original study started in 1965 and linking them with cancer and death registers and electoral rolls.

Dr Green's initial study was never formally ended but, after clinicians raised concerns, women stopped being referred for enrolment by 1975.

Once described as one of world's 25 outstanding physicians, Dr Green believed the pre-cancerous condition did not automatically lead to cancer and that radical treatment like hysterectomies could be avoided.

The Lancet article described the analysis as "a unique opportunity" arising from the unethical study.

"This study provides the most valid direct estimates yet available of the rate of progression from CIN3 to invasive cancer," the researchers said.

They noted that the risk in women not treated might be higher, because in some cases the small punch or wedge biopsies taken from abnormal lesions might have cured some women.

The women's treatment was reviewed in a seven-month judicial inquiry by Dame Silvia Cartwright in 1987-88, which concluded the study was unethical.

Dame Silvia found that some patients had received inadequate treatment, and in some cases the women had died as a result.

Dr Green and three other doctors were charged with multiple cases of disgraceful conduct by the Medical Council, although Dr Green's charges were later dropped, because he was not mentally or physically fit. He died in 2001.

Auckland woman Clare Matheson, a central figure in a court case claiming damages from National Women's, said later it was the health system that had failed by allowing the experimental research to go ahead.

31% with minimal treatment (the "unfortunate experiment")
1% with conventional treatment (usually a cone biopsy)