Instead, he told her to come back if symptoms persisted, the decision released today shows.
Five months later, the woman returned and was examined by a different doctor at the medical centre. The GP identified the lump and made an urgent referral for the woman to see a specialist.
Only then was the woman diagnosed with advanced breast cancer - but it was too late and she died.
Breast Cancer Foundation research manager Adele Gautier said this wasn't the first time something like this has happened.
"Unfortunately, this is more common than anyone would want.
"Because breast cancer is more common the older you get that risk often isn't taken seriously enough and because some woman do have lumpy breasts or cysts that come and go it's not taken seriously," Gautier said.
She said any breast lump should be referred to a specialist, even if there is a low likelihood - it's up to a breast clinic to decide where to take it from there, not a GP.
"The sad thing is many general practices don't do regular breast testings so they don't know what a breast cancer lump feels like."
Hill said by failing to refer the woman for further imaging of the lump on her breast in the circumstances, the GP failed to provide services with reasonable care and skill.
During the investigation it was discovered the medical centre did not have its own formal policies and protocols regarding clinical examinations, documentation of consultations or referrals.
Instead doctors had access to a database called HealthPathways which guides management of situations similar to this woman's case.
The commissioner told the doctor to apologise to the family for failing to refer the woman to a specialist for further imaging of a lump on her breast.
The GP has also been ordered to report back to the Health and Disability Commission following further training and any changes the practice has made as a result of this case.
The Herald understands the GP is still practising.
HDC notified the Medical Council and Health Quality and Safety Commission about this case.
Rest home failures:
Another HDC decision today revealed an elderly man died after suffering nearly 100 falls under an Auckland rest home's care during a 10 month period - that's around two falls each week.
Deputy Health and Disability Commissioner Rose Wall found Radius Residential Care Limited in breach for failing to provide adequate supervision.
Wall said although interventions were put in place to manage his risk of falling, they were not successful and the rest home's management of the man's falls risk was inadequate.
"While some interventions were implemented and some reviews were completed, there was no detailed analysis of the data collected about his falls," Wall said.
The commissioner told the rest home to apologise to the man's family for the failures. An audit to assess compliance with their policies and procedures was also recommended.
Radius Residential Care Limited were also ordered to provide HDC with evidence of their policies and procedures on falls management.
