Labtests failed to diagnose cancer in tissue taken from a patient with a history of malignant melanoma.

A 64-year-old Aucklander is upset at what his surgeon calls "an incredibly unusual" laboratory lapse.

Labtests declined to discuss the case publicly last night.

It was publicised by GP Carmel Built who, with her medical partner Dr Ian Rapson, is campaigning for Auckland's district health boards to give at least half of the region's community laboratory work to Diagnostic Medlab.

They organised an anti-Labtests meeting last week attended by about 60 doctors, all but one of whom expressed no confidence in the company.

The DHBs, which had dropped DML in favour of cut-price provider Labtests, last month gave DML back 10 per cent of the work, including all testing for private specialists, because of Labtests' ongoing problems.

The 64-year-old, who asked not to be named, was diagnosed with melanoma last November. He had surgery to remove the "black dot" from his abdomen and lymph nodes from under his arm.

Then last month he had another operation, this time to remove lymph nodes from his groin after he noticed a lump and a specialised x-ray scan showed an abnormality. The surgeon sent the tissue to Labtests.

Dr Built says in a letter to Health Minister Tony Ryall, in which she appeals to him to urgently intervene in the laboratory fiasco, that Labtests' initial findings were of no evidence of malignancy.

The surgeon confirmed this to the Herald last night and said he requested a re-analysis. This showed melanoma had spread to several of the groin nodes.

The tissue was later sent to DML, at the patient's request, and a greater degree of cancer was found.

The patient was incensed by what he called the "diabolical" initial finding by Labtests and said he had made a complaint to Health and Disability Commissioner Ron Paterson.

He now anticipated more surgery would be needed and did not yet know what his outlook might be, although he hoped he "should be able to get five years".

The surgeon said he was surprised by the first Labtests result.

"It's very unusual, incredibly unusual ... for [a pathologist] not to find disease when it's there, particularly the degree of disease that was there. I have not had this experience before. It's not the standard that we would expect."

He asked for the second opinion because a needle biopsy had indicated cancer was present and during surgery his feeling was that more than one node would be positive for cancer.

Labtests said any issues raised by referring clinicians were investigated thoroughly through the proper channels.