TPO and adenoma: Table 1 shows the correlation between H&E morphology and TPO immunoreactivity on all 424 biopsies. One lesion turned out to be a paraganglioma of nonthyroid origin and hence TPO negative. This benign tumour was not subsequently removed. All the malignant, the one suspicious and two of the seven atypical lesions were TPO negative. Five biopsies with ‘atypia’ and eight with ‘adenoma’ contained oncocytic cells, which tended to give a spotted, irregular TPO staining (Fig. 3).