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Shan Inglis, 49, discovered after an exploratory operation last month that she had papillary thyroid carcinoma, the most common form of thyroid cancer, the New Zealand Herald reported.
However, Mr Brown said his wife had requested he continue his campaign for the Auckland mayoralty.
The results came through at the same time Mr Brown was being heavily scrutinised over his council credit card use.
Ms Inglis will undergo treatment to remove malignant tissue and radiation treatment. The cancer she is suffering from has a high survival rate.
Her cancer comes two years after Mr Brown nearly died from a heart attack.
"We know what it is like to deal with tough family health issues, and we know that recovery is best served by taking a positive approach in which we offer Shan every support while continuing to function as close to normal as is possible," Mr Brown said.