Mathematical model predicts breast tumours grow faster in younger women

In collaboration with the Press Association

Norwegian researchers have published details of a new estimation method, which can be used to estimate the rate of growth of breast tumours among a population.

The model also predicts the proportion of breast cancers of a particular size which are detected at mammography screening (the "screen test sensitivity"), and its authors propose that it is nearly twice as accurate as the Markov model currently used to predict tumour progression.

The work could help health professionals and governments better understand and improve breast screening programmes. It also sheds light on the variation in how breast cancers grow.

The model was drawn up by analysing breast screening results from nearly 400,000 women taking part in the Norwegian Breast Cancer Screening Programme.

Scientists at the Cancer Registry of Norway applied their model to cancer incidence and tumour measurement data from 395,188 women between the ages of 50 and 69 years.

The results revealed that tumour growth rates vary considerably between patients, particularly in relation to age. In general, the model suggests breast tumours grow more quickly in younger women and the growth rate typically slows as the age at diagnosis increases.

Other studies, including one by the Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, have also suggested that younger women's tumours grow faster.

According to the Norwegian results, around one in 20 tumours doubles in size from 10 to 20mm in diameter in little more than a month, while a similar proportion takes more than six years to grow to the same size.

The average time required for a breast tumour to double in size to 20mm was 1.7 years.

Harald Weedon-Fekj?r, from the Cancer Registry of Norway's Department of Etiological Research, said that the new model had "enormous implications" for understanding the sensitivity of breast cancer screening programmes.

"We found that mammography screen test sensitivity increases sharply with increased tumour size, as one might expect. Detection rates are just 26 per cent for a 5mm tumour but increase to 91 per cent once a tumour is 10mm in size," he revealed.

Details of the model are published in the open access journal Breast Cancer Research.