Five percent of breast tumors may double in month

By Michael Kahn

LONDON (Reuters) - Five percent of breast cancer tumors appear to double in size in just over a month, Norwegian researchers said on Thursday in a study underscoring the potential benefits of more frequent screening.

The study published in the journal Breast Cancer Research also suggested detection rates of just 26 percent for a 5 mm tumor, and 91 percent for a 10 mm tumor.

The researchers used a computer model fed with national screening and cancer data to calculate how quickly tumors grow and estimate the proportion of breast cancers detected at screening.

This data on nearly 400,000 women aged 50 to 69 helped them estimate that about 5 percent of tumors may double in just over a month, growing from 10 mm to 20 mm. This was mainly among younger women in the study's age group.

Another 5 percent of tumors took more than six years to grow to the same size, according to the data collected before and after Norway began national breast cancer screening in 1995. This was mostly among older woman in the study.

"The variation was larger than what I was expecting," said Harald Weedon-Fekjaer, a statistician at the Cancer Registry of Norway, who led the study.

"Now we can be more certain about estimates."

The researchers used a complex formula that took into account what size tumors were when detected, measurements of surgically removed tumors and other data.