The younger a woman is when she is diagnosed with breast cancer, the faster her tumors will grow, according to a new study.

Researchers from the Cancer Registry of Norway were looking to see how tumors grow in order to improve cancer screening and testing.

They looked at data from nearly 400,000 women between ages 50 and 69 for the study.

One finding was that one in 20 tumors doubles in size in just over a month, while another one in 20 can take six years to do so.