At 36 and a mother of two young children, Pixie, 4, and Hunter, 2, Jacenko believed she was an unlikely candidate, despite being in the at-risk category following her mother Doreen Davis' mastectomy a decade ago for the same disease.

The Sweaty Betty publicist says she regrets not being more pro-active and urges all women to "be vigilant with self-examination".

"Don't just happen to be showering and come across a lump like I did," she told Fairfax Media.

"I should have known better and I should have done routine mammograms knowing that my mum had suffered from breast cancer – but I didn't, I just thought, 'I'll worry about that when I am 40 plus'.

"Even when you think, 'that will never happen to me,' one day you could wake up to start the day and it will – just like me."

Jacenko underwent an MRI on Tuesday and a second core-needle biopsy (a test to remove tissue or fluid from the suspicious area) on Wednesday. She was due to meet a specialist on Friday to discuss the next steps with regards to surgery and treatment.

The businesswoman, who is known for her strong work ethic, even tending to calls and emails just hours after giving birth to both children, says it will be business as usual for the time being.

"As to slowing down, make no mistake, if I felt unwell, I would, as one cannot get better if they don't rest and take things slower, but I don't feel unwell," she said.

"Now is about finding out how to tackle the cancer, and until treatment starts, I will be going about life as normal and then assess what I can and what I can't manage as, and when it happens."

Breast cancer is the most commonly diagnosed cancer among women in Australia, with an estimated 15,934 women and 150 men expected to be diagnosed this year.

Cancer Council Australia CEO, Professor Sanchia​ Aranda, said the disease does not discriminate.

"Those most at risk of breast cancer are women who have breasts," she said.

Jacenko discovered the lump on her left breast two weeks ago, eight days after her husband Oliver Curtis, 30, was sent to prison for two years for conspiracy to commit insider trading.

"The timing is extraordinary," she told News Corp.

Meanwhile, Curtis' legal team has filed an application to have his conviction overturned. It will be mentioned in the Court of Criminal Appeal on July 21.

What to look for when checking your breasts:

• A lump, lumpiness or thickening.
• Changes to the nipple, such as a change in shape, crusting, a sore or an ulcer, redness, unusual discharge, or a nipple that turns in (inverted) when it used to stick out.
• Changes to the skin of the breast, such as dimpling of the skin, unusual redness or other colour changes.
• Increase or decrease in the size of the breast.
• A change to the shape of the breast.
• Swelling or discomfort in the armpit.
• Persistent, unusual pain that is not related to your normal monthly menstrual cycle, remains after a period and occurs in one breast only.