A second major cancer study in the US has been discredited after data had been falsified. The news follows the revelation just a month earlier that the biggest survey on breast cancer in North America contained false data.

The latest discovery has resulted in the resignation of the research project chairman Bernard Fisher and the suspension of new patient recruitment to the study groups. The survey, into the breast cancer drug tamoxifen, has also been stopped temporarily.

The National Women's Health Network in the US wants to see the research programme abandoned, having lost faith in the American National Cancer Institute.

The NCI has admitted that its handling of falsified data has been lax. Its admission follows the revelation that part of the data in the 1985 study had been falsified. The conclusions of the survey changed the way American doctors treated breast cancer, shifting from mastectomy to lumpectomy plus radiotherapy for early-stage cancer.

Hurried research after this discovery which excluded the fraudulent data, came to a similar conclusion.

In the latest controversy, Dr Fisher has been accused of withholding data about tamoxifen and its association with the development of endometrial cancer. Informed consent forms, which women have to read and sign before agreeing to join the trials, apparently did not include the latest data showing that four women died after taking tamoxifen.