Encapsulated papillary oncocytic neoplasm of the thyroid, EPON
Definition
Encapsulated thyroid tumours comprising oncocytic cells with an at least focally papillary architecture without the nuclear features of usual papillary thyroid carcinoma. They may be subdivided into those without capsular or vascular invasion; oncocytic (Hurtle cell) adenoma with papillary growth and those with such invasion; minimally invasive oncocytic (Hurtle cell) carcinoma with papillary growth.
These tumours are more common in women and are found across a wide adult age range.
The cells are oncocytic. The architecture is variably papillary, follicular and solid. The columnar cells lining the papillary fronds with variable hobnailing. Less often, the cells are tall without hobnailing. Nuclear chromatin is finely dispersed with small nucleoli. The nuclear features of usual papillary thyroid carcinoma are rare, namely nuclear clearing, grooving, overlap and pseudo inclusions. There may be capsular or vascular invasion. Mitoses are lacking.
| HBME-1 | 0/131 | ||
| CK19 | 1/131 | ||
| CD56 | 6/71 | ||
Molecular pathology
There are no BRAF point mutations or RET/PTC rearrangements.
The prognosis is generally good.
©SMUHT/PW Bishop