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The Tauranga-based MP said in a Facebook post she was diagnosed after a regular mammogram showed "irregular calcifications".
Breast calcifications are small calcium deposits that develop in a woman's breast tissue.
"It's been a tough couple of months as I've had to cancel out of a number of appointments, and for that I apologise," she said.
"I've tried to keep my commitments where I have been able to.
"Jacinda Ardern and my colleagues have been incredibly supportive."
Tinetti also said thanked her medical team at Grace Hospital.
"Today I head home and am taking a few weeks to rest and recuperate ... Thanks to everyone for your love and support."
Tinetti told the Bay of Plenty Times she would be straight back into campaigning for the 2020 general election as soon as her rest and recuperation period was over.
"I intend to get right back into the swing of things for the campaign next year ... My recovery will take probably six weeks," she said.
This meant she would only miss one block of sitting in Parliament.
"I have the full support of our fantastic Prime Minister to take some time out now ... I'll be taking the summer and I intend to get back into things, at this stage, as long as my recovery goes well, at the end of January," she said.
She said her diagnosis showed how important it was for women to get regular mammograms.
"There was no lump ... it shows the importance of regular mammograms and why we actually go," she said.
Tinetti was elected in the 2017 election as a Tauranga list MP. She is the deputy chairwoman of the Education and Workforce Committee.
She is also the former principal of Merivale School, Tauranga's sole decile 1 school.
Commenters on the Facebook post have offered their support to Tinetti since the announcement this evening.
National Leader Simon Bridges, who is also the Tauranga MP, said he was sorry to hear the news and was thinking of Tinetti at this time.
"I hope for a swift and full recovery."