However, he then suddenly asked her if she performed regular breast examinations.
"I replied by saying 'no'," the woman said.
"This comment was out of the blue and nothing about the topic had been discussed at this point. I have never before been asked about breast cancer during a check up," the woman told the tribunal in the hearing.
She said the doctor then asked her if she should be and she replied that there was no history of breast cancer in her family.
He told her it was important that he would show her how to do it, raising his own arm giving a demonstration.
The doctor then walked towards her and "prodded" her left breast outside of her clothing.
The woman said the doctor never told her was going to touch her breast or any information about the proposed examination.
The doctor's hand moved down from above the height of her bra until he was touching the outside of her bra.
"He began holding and squeezing my breast," the woman said. "He then realised I had a bra on and told me that it does not work as well with a bra on, he said it is not good medical practice. He was touching my left breast for about 20 seconds."
The doctor didn't mention or touch her right breast and she was not offered to have another staff member present.
The doctor admitted touching the woman's breast area, but categorically denied that it was inappropriate or for an improper purpose.
"[I]n so far as my teaching or understanding of medical practice is concerned, I understand that self-breast examination is encouraged in the 20 to 30 year old patient group — as much as anything else to encourage patients to get into the habit of knowing or identifying when there has been tissue change.
"This is something I understand the Breast [Cancer] Foundation of New Zealand indeed recommends."
The doctor noted to HDC his "genuine apology and regret that [the woman] has misinterpreted his behaviour and intentions".
Independent expert Dr Clare Woodward was asked to provide her view and said the GP's actions were " a significant departure from standard practice", in regards to the way her breast was examined, the fact she didn't give consent, was not offered a chaperone, wasn't behind a curtain, was examined fully clothed and just one breast.
"She came for a diabetes check up and didn't request a breast check. It is unusual to perform a breast check on a 20 year old female unless she has a specific problem she is worried about."
The commissioner found the GP in breach of two parts of the code; failing to provide the woman with the information that she was entitled to receive, and the woman not being in a position to make an informed choice as she wasn't given information she was entitled to receive.
The commissioner was also critical that there was no clinical indication to warrant the demonstration of a breast examination on the woman, and that the GP did not adhere to standard practice when examining the woman's breast.
The commissioner recommended that should the GP return to practice, the Medical Council of New Zealand consider whether a review of the GP's competency was warranted.
The GP had given an apology to the woman.