Undifferentiated Malignant Neoplasm Involving Parotid and Thyroid: Sampling and PAX8 Cross-Reactivity Can Obscure the Diagnosis of Lymphoma

Figure 4

Isthmusectomy specimen demonstrates sheets of malignant cells displacing thyroid follicles; neoplasm is clearly pancytokeratin-negative with coexpression of PAX5 and polyclonal PAX8 immunoreactivity.

(a) Resection, 100x magnification, H&E stain

(b) Resection, 100x magnification, pancytokeratin immunostain

(c) Resection, 100x magnification, PAX5 immunostain

(d) Resection, 100x magnification, PAX8 immunostain