Women with extremely dense breasts have a four-to-six fold increased risk of breast cancer and are at greater danger of having a potential tumour missed.

A mammogram won't always detect a tumour in women with very dense breasts, experts warn.

Thousands of Australian women, almost eight per cent, aged 40-74 years have dense breasts - that is breasts with less fatty tissue and more glands that make and drain milk.

These women are four to six times more likely of developing breast cancer.

Even more concerning is that they are at greater risk of a potential breast cancer tumour going undetected.

Associated Professor Wendy Ingman from the Univeristy of Adelaide says on a mammogram breast density looks similar to potential tumours.

"The danger is that these women are at risk of having tumours missed at the time of screening," said Prof Ingman.

Breast cancer is the most common cancer in women in Australia and the second most common cancer to cause death in women, after lung cancer.

An estimated one in eight women are diagnosed with breast cancer by age 85.

One woman touched by breast cancer was the late Australian rock music icon Chrissy Amphlett.

The Divinyls frontwoman lost her battle with the disease in April, 2013, at the age of 53.

In tribute to Amphlett and to coincide with Breast Cancer Awareness Month, underwear brand Berlei has partnered with the I Touch Myself Project - to release The Chrissy Bra range.

The range of bras include The Chrissy T-Shirt Bra and The Chrissy Post-Care Bra - for those women who have had breast cancer surgery.

All profits go to Breast Cancer Network Australia.

Women are advised to go to their GP to have their breast density assessed and continue to have regular mammograms through BreastScreen services.