The oncologist recommended three cycles of chemotherapy rather than six because of the relatively low grade of cancer.
However, at a multidisciplinary meeting involving the gynaecologist, pathologist and other doctors the woman's stage of cancer was upgraded to the more serious Stage 2C3.
The report was sent to the oncologist at the cancer clinic but did not mention there had been a change in the rating of the cancer.
The oncologist received the report but noticed another patient's details had been attached, so asked for it to be corrected and expected it would be sent back to her. It never was.
Neither the woman or her GP were notified of the change in classification of the cancer.
The gynaecologist assumed she was getting six rounds of chemotherapy and later referred her to the district health board's Gynaecology Oncology Services for monitoring but mistakenly used the initial lower classification in his referral.
In May 2015, a blood test showed her cancer marker levels were above the normal range but the gynaecologist did not inform her of the results.
In August, the woman went to her GP with discomfort in her right chest and further tests were done.
The first time she was told her cancer had been upgraded to a more serious stage was in September. During the same meeting she was told she now had incurable cancer.
Deputy Health and Disability Commissioner Rose Wall said the gynaecologist failed the woman by not ensuring the oncologist was advised of the change, by not noticing the woman's cancer kept being referred to as a lower grade and not making sure the woman was told of the upgraded cancer stage.
She recommended that the gynaecologist provide the woman with a written letter of apology and that the Medical Council of New Zealand consider whether a review of the gynaecologist's competence was required.
Wall was also critical of the oncologist for not noticing the discrepancy between the stage of the cancer and the pathology information and for not following up the report when it was not returned to her. Wall also criticised the cancer clinic for the administrative error which meant the report was not sent back to the oncologist.
Wall recommended that Ascot Central Women's Clinic review its multidisciplinary meeting process significantly to make sure relevant results were passed on and that the clinic provide the woman with a written letter of apology.
She also recommended the DHB consider reviewing its protocols and procedures in relation to the treatment and follow-up of cancer patients who were transitioning between the private and public sector.