PURPOSE: @entity3243 ( @entity3243 ) is remarkable for its rare occurrence and challenging diagnostics. @entity3243 accounts for 0.1-5  % cases of @entity459 ( @entity459 ). The differentiation from @entity5 is difficult even by morphological criteria. To address these issues, we assessed the @entity3243 frequency in two separate European @entity459 cohorts and evaluated the demographic, clinical, morphological and molecular background. METHODS: A retrospective study was carried out, using continuously maintained database (2005-2014) of @entity459 @entity1 from two tertiary referral university hospitals in Europe. The demographic, clinical data and frequency of @entity3243 among surgically treated @entity459 was detected. Immunohistochemistry (IHC) was performed to detect parafibromin, representing protein product of @entity15966 gene and proliferation marker Ki-67. RESULTS: Both @entity459 cohorts were characterised by close mean age values (58.6 and 58.0  years) and female predominance. The frequency of @entity3243 differed significantly between the cohorts: 2.1 vs. 0.3  %; p   =   0.004. @entity3243 was characterised by invariable complete loss of parafibromin contrasting with @entity3243 . The proliferation fraction was similar in both @entity3243 cohorts (10.6 and 11.0  %). @entity3243 showed significantly higher proliferation fraction than typical @entity3243 (1.6  %), atypical @entity652 (1.6  %) or @entity652 featuring focal loss of parafibromin (2.2  %). CONCLUSIONS: @entity3243 frequency can range significantly between the two European cohorts. The differences can be attributable to selection bias of @entity1 referred for surgery and are not caused by discordant definition of malignant parathyroid histology. Diffuse loss of parafibromin and increased proliferation fraction by Ki-67 are valuable adjuncts in @entity3243 diagnostics due to significant differences with various clinical and morphological subtypes of @entity652 .

Evaluation of malignant @entity5 in two European cohorts of XXXX with sporadic @entity459 .

@entity1 :: ('9606', 'Species') :: ['patients'] @entity459 :: ('MESH:D049950', 'Disease') :: ['primary hyperparathyroidism', 'PHPT'] @entity5 :: ('MESH:D009369', 'Disease') :: ['benign tumours'] @entity3243 :: ('MESH:D010282', 'Disease') :: ['PC', 'Parathyroid carcinoma', 'parathyroid adenomas'] @entity652 :: ('MESH:D000236', 'Disease') :: ['adenomas', 'adenoma'] @entity15966 :: ('79577', 'Gene') :: ['HRPT2']
@entity1 :: (9606,Species) :: ['patients']
