Massachusetts is the 18th state to pass breast density legislation, according to the Are You Dense advocacy group. The legislation aims to protect Massachusetts women from the consequences of missed, delayed, and late-stage breast cancer diagnoses. The bill was inspired by former Somerville resident Ellen Kelleher, whose cancer was missed by mammography. She died in 2013 before the bill could become law, Are You Dense said.

Kelleher's husband, her attorney, and other Massachusetts dense breast tissue reporting advocates shepherded the bill through the legislature, the organization said.