'Very likely there': Dense breasts hid woman's cancer from mammogram

Rachael's routine mammogram came back clear, but five months later a biopsy taken ahead of her breast reduction surgery found cancer that had likely been hiding in her dense breast tissue.

"What is understood now is that that tumour was very likely there but wasn't picked up," she said.

Dense breast tissue can affect anyone, but age, genetics and hormone treatments can play a part.

Radiologist Dr Monica Saini explained why density makes cancer harder to spot.

"This dense tissue looks white on a mammogram and cancer looks white, so you can imagine that if you have more white it's harder to find cancer in that background."

A decade ago, Saini began offering contrast enhanced mammography to cancer patients. The scan pairs a standard mammogram with a dye injected into the bloodstream, which makes tumours easier to see.

A small number of clinics offer the technology, mostly privately, and usually only to patients already diagnosed or considered high risk.

Women with high breast density alone are not classed as high risk, despite what the evidence suggests.

"That risk is anywhere from two to four times increased from a woman who has extremely dense breasts compared to a woman who mostly has fatty breast tissue, and that's a risk over her lifetime," Saini said.

Health NZ's guidelines for public breast screening do not require density to be recorded, or for women to be told about it.

The agency reviewed how density reporting could be included in screening last year.

Alana Ewe-Snow, from Health NZ's National Public Health Service prevention screening team, said the agency was still working out what it would need to introduce breast density measurement and reporting within BreastScreen Aotearoa.

"This includes consideration of service impacts, workforce and imaging capacity requirements, and the availability of appropriate follow-up pathways.

"As part of this, BSA will also need to carry out research to determine what proportion of women have different breast densities in Aotearoa New Zealand."

The Breast Cancer Foundation wants contrast enhanced mammography made available to women like Rachael who have dense breast tissue.

"The sooner we actually identify and get people on a treatment programme, we save lives," chief executive Vanessa Sorenson said.

Rachael is now in remission. Had the tumour not been found, she would have waited another 18 months for her next mammogram.

"It was close to the chest wall and I suspect that things would be looking very, very different right now."

The Royal Australian and New Zealand College of Radiologists updated its guidelines in 2024 to recommend mandatory reporting of breast density in both screening and diagnostic settings.