Wednesday, April 7, 1999 Published at 13:22 GMT 14:22 UK
Breast cancer 'more than one disease'
Researchers do not know why some women get different tumours
Breast cancer may not get progressively worse - it could just be that there are different types of tumour, researchers have found.
Breast cancer tumours known as ductal carcinomas are graded from I to III, where grade I is the least aggressive.
Doctors had thought that grade I tumours eventually grew into grade III tumours.
But the new research strongly suggests that the different grades are actually distinct forms of breast cancer.
The finding could lead to better-targeted research to tackle the disease.
Several types of breast cancer
Dr Rebecca Roylance and colleagues conducted the research at the Imperial Cancer Fund's Human Cytogenetics and Breast Pathology Laboratories.
Dr Roylance said: "It was about 10 years ago that people began to question the meaning of these grades.
"This isn't what you'd expect if tumours were progressing."
Her team compared the genetic make-up of 40 grade I tumours with that of 50 grade IIIs.
They found that genetic changes found on grade I tumours were not always found on grade III tumours.
While grade III tumours may well have more genetic changes and losses than grade I tumours.
But if there is progression, then all the differences found on grade I tumours should also exist on grade III.
This was not always the case - for example, 65% of grade I tumours had lost part of chromosome 16, but this was the case in only 16% of grade III tumours.
Reasons for the differences
Dr Roylance said: "It's unclear why some women get a grade I and others a grade III tumour, but it's likely there will be more than one reason.
"Grade I tumours occur more often in older people, and it could be that their causes are quite distinct from those of grade III tumours, which are relatively more common in the young.
"Breast cancer has usually been investigated as one disease, so these findings have implications for past research on this group of tumours.
"Our study provides a framework for the further study of the molecular basis of breast cancer."
Dr David Miles, of the ICRF's Breast Biology Group at Guy's Hospital in London, said the research could focus future treatments.
He said: "We hope that in future the ability to profile tumours in terms of their genetic material will give us a better understanding of their behaviour.
"This will allow us to make more accurate predictions of the effects of conventional treatment, and also aid in the design of new therapies."