The oncocytic variant of papillary thyroid carcinoma with multifocal involvement: a case report

In the most recent World Health Organization International Histological Classification of Thyroid Tumors, Hedinger and colleagues have defined papillary thyroid carcinoma as “a malignant epithelial tumor showing evidence of follicular cell differentiation, with typical papillary and follicular structures as well as characteristic nuclear changes”.[,,] This variant accounts for 1-11% of all cases of thyroid PC; the differences among reported series are probably result of application of different classification criteria.[,] Furthermore, histopathological criteria for diagnosis and biological behavior of the oncocytic variant of PC have remained poorly defined.[,]

The diagnosis of oncocytic variant of PC remains controversial. Oncocytic PCs may have papillary or follicular architecture. The papillary type is characterised by complex branching papillae in which oncocytic cells cover thin fibrovascular stromal cores. Oncocytic PC with follicular architecture may be macrofollicular or microfollicular with variable colloid storage. The oncocytic cells are usually polygonal but may be columnar; they have abundant granular, pale, eosinophilic cytoplasm. The diagnosis of papillary differentiation is based on the nuclear features of these lesions. Berho and Suster proposed that the diagnosis of oncocytic PC should be based primarily on nuclear features like the typical optically clear nuclei with the characteristic intranuclear cytoplasmic inclusions and the presence of nuclear grooves. These features are currently attributed to be more important than the presence of papillae as diagnostic criteria for PC.[-,] The nuclear features determined in our case supported the diagnosis of oncocytic PC. It is important to identify these features in well delineated lesions with follicular architecture.[,,,]

Recently, an unusual oncocytic PC partly cystic type with abundant lymphoid stroma, that is bearing a resemblance to “Warthin's tumor of salivary gland” has been described.[,] The “Warthin-like” tumor has abundant chronic inflammatory cells and is freguently associated with Hashimoto's thyroiditis.[-] The extensive lymphocytic infiltration in oncocytic PC and their association with chronic lymphocytic thyroiditis, may suggest the role of immunological mechanisms in the pathogenesis of thyroid tumors,[,,] rather than the expression of the inherent biological characteristics of the tumor cells.[] There was focal peritumoral lymphocytic thyroiditis in our case. In addition to these findings, we designeted the pattern of multifocal growth which is actually rarely encountered.[]

The reported clinical behavior of oncocytic tumors is variable. In the 1950s, the American Cancer Society recommended to classify all thyroid tumors with oncocytic features as malignant. Since then, most studies have indicated that oncocytic neoplasm can be classified into adenomas and carcinomas by using the morphological criteria that is valid for follicular non-oncocytic tumors. [,,] The overall mortality rate of oncocytic carcinoma (both follicular and papillary) was said to be considerably higher than that of non-oncocytic tumors.[,,,] Herrera et al. defined that oncocytic variant of PC should be more widely recognized as a tumor variant with a truly more aggressive biologic behavior as confirmed in previous studies. [] On the contrary, Berho and Suster believed that these lesions appeared to have a low-grade clinical behavior akin to conventional PC.[] The study of Cheung et al, which depends on molecular basis of Hurthle cell PC, indicated that this tumor may behave in a fashion analogous to typical PC.[]

The oncocytic variant of papillary thyroid carcinoma, although rare, appears to represent a morphologically distinctive variant of papillary cancer. Application of strict histological criteria is therefore necessary to distinguish these lesions from other primary thyroid neoplasms that is characterized by similar oncocytic cytoplasmic features.[,,] Further research is needed for the management of oncocytic variant of papillary carcinoma of the thyroid.