A B.C. woman whose dense breast tissue may have masked a cancerous tumour growing inside her has launched a petition to prevent other women from suffering the same fate.

Elizabeth Astbury discovered an eight-centimetre lump in her breast in April 2013, despite getting regular mammograms for years.

“I was diagnosed with Stage 3 breast cancer,” she said. “I was shocked, devastated.”

Astbury eventually beat her cancer with a mastectomy, chemotherapy and radiation, but wondered by her mammogram didn't detect her tumour.

She soon learned mammograms have a harder time detecting cancer in women with dense breast tissue, a discovery that’s sparked a growing push in the U.S. to inform patients before it’s too late.

Fourteen states already have legislation requiring doctors to inform women if they have dense breasts, but no such policy exists in Canada.

Astbury wants that to change, and her petition is calling for B.C. to step up to the plate first.

“If in 2010 I had got a letter saying, ‘Your breasts seem to be really dense, come back for an ultrasound,’ I could be in a different place now,” she said.

Ultrasounds are considered a valuable diagnostic tool in addition to mammograms in the health care community, but not as a replacement. Even mammograms miss about 25 per cent of malignant tumours.

The B.C. Cancer Agency won’t commit to any new policy but said it will study if new 3D screening can improve detection in women with dense tissue.

In the meantime, Astbury, who has a 35 to 40 per cent chance of recurrence, is dedicated to making sure other women have access to the information she didn’t.

“It could make a huge difference,” she said. “Early detection is absolutely crucial.”

To sign Astbury’s petition, visit her website.

With a report from CTV Vancouver’s Mi-Jung Lee