Loss of Nuclear Expression of Parafibromin Distinguishes Parathyroid Carcinomas and Hyperparathyroidism-Jaw Tumor (HPT-JT) Syndrome-related Adenomas From Sporadic Parathyroid Adenomas and Hyperplasias

Abstract

Parathyroid carcinoma is notoriously difficult to diagnose with confidence in borderline cases. Commonly there is a long lag time between diagnosis and clinical evidence of malignant behavior even in histopathologically straightforward lesions. There is therefore a need for a novel adjunctive marker to assist in the diagnosis of carcinoma. Parafibromin is the protein encoded by the putative tumor suppressor gene HRPT2. Mutations predicted to inactivate parafibromin were first detected in the germline of patients with hyperparathyroidism-jaw tumor (HPT-JT) syndrome. Subsequently, somatic mutations have been identified in the majority of sporadic carcinomas. We performed immunohistochemistry for parafibromin on 115 parathyroid tissues comprising 4 HPT-JT-related tumors (3 adenomas and 1 carcinoma), 11 sporadic parathyroid carcinomas, 79 sporadic adenomas, 3 multiple endocrine neoplasia 2A-related adenomas, 2 sporadic primary hyperplasias, 2 multiple endocrine neoplasia (MEN)-1-related hyperplasias, 6 secondary hyperplasias, 4 tertiary hyperplasias, and 4 normal parathyroid glands. There was complete absence of nuclear staining in 3 of 4 (75%) HPT-JT-related tumors and 8 of 11 (73%) sporadic parathyroid carcinomas and focal weak staining in 1 of 4 HPT-JT tumors and 2 of 11 sporadic parathyroid carcinomas. Only 1 parathyroid carcinoma exhibited diffuse strong nuclear expression of parafibromin. In contrast, 98 of 100 non-HPT-JT-related benign parathyroids showed diffuse strong nuclear positivity and 2 of 100 showed weak positive staining. We conclude that, in the correct clinical and pathologic context, complete absence of nuclear staining for parafibromin is diagnostic of parathyroid carcinoma or an HPT-JT-related tumor.

Parafibromin immunoreactivity: its use as an additional diagnostic marker for parathyroid tumor classification

“…In our experience, antigen retrieval by heating in citrate buffer was necessary to obtain a distinct nuclear signal without interfering background, in agreement with previous publications (Tan et al 2004, Gill et al 2006. For the monoclonal antibody 2H1, the following parameters were tested: antibody dilution (1:20, 1:100, and 1:200), antigen retrieval time (10, 20, 30, and 50 min) as well as incubation time (1 h and overnight).…”

“…Since adenomas in turn are much more frequent than carcinomas, the negative predictive value (i.e. the chance that an adenoma is correctly identified by positive parafibromin staining) would end up as high, although probably not 100% since reduced expression of parafibromin has been reported in small subsets of parathyroid adenomas (Gill et al 2006, Juhlin et al 2006. Hence, in parathyroid tumors with positive parafibromin expression, the risk of malignancy is very low, however, cannot be fully excluded.…”

“…In immunohistochemical studies of unequivocal and HPT-JT-related carcinomas, complete loss, or reduced nuclear immunoreactivity was found in the majority of cases. By contrast, 98-100% of unselected sporadic adenomas stained completely positive (Tan et al 2004, Gill et al 2006. In a subset of cystic adenomas, loss of parafibromin has been associated with HRPT2 mutations (Juhlin et al 2006).…”

Defining a molecular phenotype for benign and malignant parathyroid tumors

“…Germ-line and somatic HRPT2 mutations have been found in sporadic and familial parathyroid carcinomas, with frequencies ranging from 65% to 100%. 25,26,30,31 Somatic HRPT2 mutations have also been found in both sporadic and hereditary adenomas related to HHJTS. 24,28,30,32 Similarly, negative parafibromin immunostaining has also been reported in sporadic and HHJTS-related parathyroid adenomas.…”

Parathyroid carcinoma

“…Most parathyroid carcinomas also exhibit aberrant immunohistochemical staining for parafibromin, the protein product of CDC73; complete loss of parafibromin expression is the most common staining pattern. As the large majority of benign parathyroid tumors (except in the setting of germline CDC73 mutation) display normal parafibromin staining, parafibromin immunohistochemistry may be considered as a diagnostic adjunct for parathyroid cancer in otherwise equivocal cases [22][23][24] but aberrant parafibromin staining alone is insufficient as a diagnostic marker of parathyroid carcinoma [25] .…”