The Shoalhaven Mayor has been diagnosed with breast cancer.

"I am normally a very private person, but I decided to go public with this to help raise awareness," Cr Gash said on Wednesday.

"This can happen to anyone, rich or poor, famous or infamous ... if it comes your way, you have to deal with it.

"Basically, there is a cancerous lump that needs to come out.

"It was discovered a couple of weeks ago through a regular breast screen.

"It totally blew me away; this has all happened very quickly.

"They will be operating on Monday ... a lumpectomy will take most of the breast, but not all, and should eliminate the need for chemotherapy," she said.

Cr Gash will know if further treatment is required a week after the operation.

The 69-year-old said she intended to take just one week's leave.

"I also want to dispel any rumours ... I have no intention of resigning and there will be no byelections.

"You don't need two good boobs to be a mayor."

Cr Gash said her sister had a mastectomy 18 years ago and was doing well.

She said women aged 50 to 74 should have a mammogram every two years.

In 2012, Cr Gash, who served as the federal member for Gilmore for 17 years, became the Shoalhaven's first female mayor, securing a record-breaking 63 per cent of the mayoral vote.

For information on breast cancer go to: cancercouncil.com.au.