Fig. 4

PTC recurrence in the laryngeal cricoid of patient 3. In a biopsy from the laryngeal cricoid solid sheets of tumor cells were seen with focal keratinisation. Panel a shows the HE stained tissue. Immunohistochemical analysis of TTF-1 (panel b) and P63 (Panel c) is shown. A large proportion of the cells stained positive for P63, supporting the squamous features. However, there was a fraction a cells that stained moderately positive for TTF-1 (thick arrow in panel b), partly overlapping with P63 positivity (thin arrow in panel c). Thyroglobulin also stained focally positive (not shown). Due to the TTF-1 and thyroglobulin positivity, we favoured the diagnosis of recurrent papillary thyroid cancer with remarkable squamous metaplasia over a primary laryngeal squamous carcinoma