['This study was undertaken to investigate the genetic factors underlying the development of multifocality and phenotypic diversity in multifocal papillary thyroid carcinoma (mPTC).', 'Loss of heterozygosity (LOH) and BRAF(V600E) mutation status were analysed in a total of 55 individual tumour foci from 18 cases of mPTC. The genetic findings and morphology of tumour foci were then compared.', 'Multifocal PTC LOH rates were higher than observed previously in solitary PTC. Different patterns of LOH and BRAF(V600E) positivity separated follicular variant tumours and tumour foci from other PTC histological subtypes. In five cases, genetic alterations were detected in morphologically normal thyroid epithelium.'] Do distinct genetic changes characterise multifocality and diverse histological subtypes in papillary thyroid carcinoma?