Loss of nuclear expression of parafibromin distinguishes parathyroid carcinomas and hyperparathyroidism-jaw tumor (HPT-JT) syndrome-related adenomas from sporadic parathyroid adenomas and hyperplasias

[Pathology of parathyroid glands: Practical aspects for routine pathological investigations]

The diagnostic histopathology of parathyroid glands comprises mostly benign diseases associated with primary, secondary and rarely tertiary hyperparathyroidism. Parathyroid adenoma and hyperplasia are the most common diagnoses, whereas parathyroid carcinomas and atypical adenomas are exceptional causes of hyperparathyroidism, the latter being purely a diagnosis by exclusion. This article deals with the major histopathological criteria of the various diagnoses with special emphasis on the clinical manifestation.

Evaluation of malignant parathyroid tumours in two European cohorts of patients with sporadic primary hyperparathyroidism

Purpose

Parathyroid carcinoma (PC) is remarkable for its rare occurrence and challenging diagnostics. PC accounts for 0.1–5 % cases of primary hyperparathyroidism (PHPT). The differentiation from benign tumours is difficult even by morphological criteria. To address these issues, we assessed the PC frequency in two separate European PHPT cohorts and evaluated the demographic, clinical, morphological and molecular background.

Methods

A retrospective study was carried out, using continuously maintained database (2005–2014) of PHPT patients from two tertiary referral university hospitals in Europe. The demographic, clinical data and frequency of PC among surgically treated PHPT was detected. Immunohistochemistry (IHC) was performed to detect parafibromin, representing protein product of HRPT2 gene and proliferation marker Ki-67.

Results

Both PHPT cohorts were characterised by close mean age values (58.6 and 58.0 years) and female predominance. The frequency of PC differed significantly between the cohorts: 2.1 vs. 0.3 %; p = 0.004. PC was characterised by invariable complete loss of parafibromin contrasting with parathyroid adenomas. The proliferation fraction was similar in both PC cohorts (10.6 and 11.0 %). PC showed significantly higher proliferation fraction than typical parathyroid adenomas (1.6 %), atypical adenomas (1.6 %) or adenomas featuring focal loss of parafibromin (2.2 %).

Conclusions

PC frequency can range significantly between the two European cohorts. The differences can be attributable to selection bias of patients 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 PC diagnostics due to significant differences with various clinical and morphological subtypes of adenoma.

The roles of parafibromin expression in ovarian epithelial carcinomas: a marker for differentiation and prognosis and a target for gene therapy

Parafibromin is a protein encoded by hyperparathyroidism 2 (HRPT2) and its downregulated expression is involved in the pathogenesis of parathyroid, breast, gastric, colorectal, lung, head and neck cancers. We aimed to investigate the roles of parafibromin expression in tumorigenesis, progression, or prognostic evaluation of ovarian cancers. HRPT2-expressing plasmid was transfected into ovarian cancer cells with the phenotypes and related molecules examined. The messenger RNA (mRNA) and protein expression of parafibromin were also examined in ovarian normal tissue, benign and borderline tumors and cancers by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, or immunohistochemistry respectively. It was found that parafibromin overexpression caused a lower growth, migration and invasion, higher sensitivity to cisplatin and apoptosis than the mock and control (P < 0.05). The transfectants showed the hypoexpression of phosphoinositide 3-kinase (PI3K), Akt, p70 ribosomal protein S6 kinase (p70s6k), Wnt5a, B cell lymphoma-extra large (Bcl-xL), survivin, vascular endothelial growth factor (VEGF) and matrix metallopeptidase 9 (MMP-9) than the mock and control at both mRNA and protein levels (P < 0.05). According to real-time PCR, parafibromin mRNA level was lower in ovarian benign tumors and cancers than normal ovary (P < 0.05), while parafibromin was strongly expressed in metastatic cancers in omentum than primary cancers by Western blot. Immunohistochemically, parafibromin expression was stronger in primary cancers than that in ovarian normal tissue (P < 0.05) but weaker than the metastatic cancers (P < 0.05) with a positive correlation with dedifferentiation, ki-67 expression and the lower cumulative survival rate (P < 0.05). These findings indicate that parafibromin downregulation might promote the pathogenesis, dedifferentiation and metastasis of ovarian cancers possibly by suppressing aggressive phenotypes, such as proliferation, cell cycle, apoptosis, migration and invasion.

Parafibromin Staining Characteristics in Urothelial Carcinomas and Relationship with Prognostic Parameters

Background:

Parafibromin is a recently defined tumor suppressor gene. The aim of our study was to determine the relationships of parafibromin expression in urothelial carcinomas (UCs) with prognostic parameters and to evaluate the use of parafibromin as a potential marker of UC.

Methods:

Parafibromin expression was assessed in 49 UC specimens using immunohistochemistry. The correlations between parafibromin expression and clinical and pathologic parameters were investigated.

Results:

Of the patients, 42 (85.7%) were male, and the mean age was 69.6 ± 8.2 years (range, 54 to 88 years). Morphologically, the UCs were divided into two groups: papillary (n = 27) and non-papillary (n = 22). There were seven low-grade (14.3%) and 42 high-grade (85.7%) tumors. Parafibromin was negative in 13 tumors (26.5%), partially positive in 19 tumors (38.8%), and positive in 17 tumors (34.7%). Parafibromin expression was more negative in UCs from upper urinary locations (n=17) and with muscularis propria invasion (n=28), which was statistically significant (p = .009 and p = .007, respectively). There was no statistically significant relationship between parafibromin expression and gender, age, tumor grade, survival, or disease-free survival.

Conclusions:

We found that UC cases with parafibromin positivity had less of a tendency to show muscularis propria invasion and were more commonly located in the lower urinary system. These results need to be confirmed with studies based on larger case series.

Parathyroid cancer

Parathyroid carcinoma is an exceedingly rare endocrine malignancy first described in 1933. It accounts for between 0.5% and 5% of all cases of primary hyperparathyroidism. Parathyroid carcinoma is unusual among endocrine malignancies, being more hormonally active than its benign counterpart. Parathyroid carcinoma poses a diagnostic challenge both clinically and histologically due to the lack of features which can definitively distinguish malignant from benign disease early in its clinical course. Here, we describe the clinical features of the disease, and present the current opinion on optimal management. Further, we analyse the most recent histological advances made to aid in the diagnosis and management of this rare, but potentially devastating, disease.

Early Onset Primary Hyperparathyroidism Associated with a Novel Germline Mutation in CDKN1B

Individuals presenting with primary hyperparathyroidism (PHPT) at a young age commonly have an underlying germline gene mutation in one of the following genes: MEN1, CASR, or CDC73. A small number of families with primary hyperparathyroidism have been identified with germline mutations in CDKN1B and those patients with primary hyperparathyroidism have almost exclusively been women who present in middle age suggesting that the age of onset of PHPT in MEN4 may be later than that of MEN1. We present a case of apparently sporadic PHPT presenting in adolescence with single gland disease associated with a novel CDKN1B germline mutation (heterozygote for a missense mutation in exon 1 of the CDKN1B gene (c.378G>C) (p.E126D)). The implication from this case is that CDKN1B germline mutations may be associated with PHPT at an earlier age than previously thought.

Clinicopathological correlates of hyperparathyroidism

Hyperparathyroidism is a common endocrine disorder with potential complications on the skeletal, renal, neurocognitive and cardiovascular systems. While most cases (95%) occur sporadically, about 5% are associated with a hereditary syndrome: multiple endocrine neoplasia syndromes (MEN-1, MEN-2A, MEN-4), hyperparathyroidism-jaw tumour syndrome (HPT-JT), familial hypocalciuric hypercalcaemia (FHH-1, FHH-2, FHH-3), familial hypercalciuric hypercalcaemia, neonatal severe hyperparathyroidism and isolated familial hyperparathyroidism. Recently, molecular mechanisms underlying possible tumour suppressor genes (MEN1, CDC73/HRPT2, CDKIs, APC, SFRPs, GSK3β, RASSF1A, HIC1, RIZ1, WT1, CaSR, GNA11, AP2S1) and proto-oncogenes (CCND1/PRAD1, RET, ZFX, CTNNB1, EZH2) have been uncovered in the pathogenesis of hyperparathyroidism. While bi-allelic inactivation of CDC73/HRPT2 seems unique to parathyroid malignancy, aberrant activation of cyclin D1 and Wnt/β-catenin signalling has been reported in benign and malignant parathyroid tumours. Clinicopathological correlates of primary hyperparathyroidism include parathyroid adenoma (80-85%), hyperplasia (10-15%) and carcinoma (<1-5%). Secondary hyperparathyroidism generally presents with diffuse parathyroid hyperplasia, whereas tertiary hyperparathyroidism reflects the emergence of autonomous parathyroid hormone (PTH)-producing neoplasm(s) from secondary parathyroid hyperplasia. Surgical resection of abnormal parathyroid tissue remains the only curative treatment in primary hyperparathyroidism, and parathyroidectomy specimens are frequently encountered in this setting. Clinical and biochemical features, including intraoperative PTH levels, number, weight and size of the affected parathyroid gland(s), are crucial parameters to consider when rendering an accurate diagnosis of parathyroid proliferations. This review provides an update on the expanding knowledge of hyperparathyroidism and highlights the clinicopathological correlations of this prevalent disease.

Parathyroid: The Pathology of Hyperparathyroidism

This review focuses on the pathologic entities associated with hyperparathyroidism in humans. A discussion of the lesions, their embryology, and pathologic features is included. Immunohistology, cytopathology, and a brief overview of molecular aspects of the lesion are included.

Hyperparathyroidism-jaw tumor syndrome: Results of operative management

BACKGROUND

Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is a rare, autosomal-dominant disease secondary to germline-inactivating mutations of the tumor suppressor gene HRPT2/CDC73. The aim of the present study was to determine the optimal operative approach to parathyroid disease in patients with HPT-JT.

METHODS

A retrospective analysis of clinical and genetic features, parathyroid operative outcomes, and disease outcomes in 7 unrelated HPT-JT families.

RESULTS

Seven families had 5 distinct germline HRPT2/CDC73 mutations. Sixteen affected family members (median age, 30.7 years) were diagnosed with primary hyperparathyroidism (PHPT). Fifteen of the 16 patients underwent preoperative tumor localization studies and uncomplicated bilateral neck exploration at initial operation; all were in biochemical remission at most recent follow-up. Of these patients, 31% had multiglandular involvement; 37.5% of the patients developed parathyroid carcinoma (median overall survival, 8.9 years; median follow-up, 7.4 years). Long-term follow-up showed that 20% of patients had recurrent PHPT.

CONCLUSION

Given the high risk of malignancy and multiglandular involvement in our cohort, we recommend bilateral neck exploration and en bloc resection of parathyroid tumors suspicious for cancer and life-long postoperative follow-up.

Familial isolated primary hyperparathyroidism/hyperparathyroidism-jaw tumour syndrome caused by germline gross deletion or point mutations of CDC73 gene in Chinese

OBJECTIVE

Hyperparathyroidism-jaw tumour syndrome (HPT-JT) and familial isolated primary hyperparathyroidism (FIHP) are two subtypes of familial primary hyperparathyroidism, which are rarely reported in Chinese population. Here, we reported three FIHP families and one HPT-JT family with long-term follow-up and genetic analysis.

DESIGN AND METHODS

A total of 22 patients, from four FIHP/HPT-JT families of Chinese descent, were recruited and genomic DNA was extracted from their peripheral blood lymphocytes. Direct sequencing for MEN1, CDC73, CASR gene was conducted. Reverse transcription PCR (RT-PCR) and quantitative real-time PCR (qRT-PCR) were used to study the effect of splice site mutations and gross deletion mutations. Immunohistochemistry was performed to analyse parafibromin expression in parathyroid tumours. Genotype-phenotype correlations were assessed through clinical characteristics and long-term follow-up data.

RESULTS

Genetic analysis revealed four CDC73 germline mutations that were responsible for the four kindreds, including two novel point mutation (c.157 G>T and IVS3+1 G>A), one recurrent point mutation (c.664 C>T) and one deletion mutation (c.307+?_513-?del exons 4, 5, 6). RT-PCR confirmed that IVS3+1 G>A generated an aberrant transcript with exon3 deletion. Immunohistochemical analysis demonstrated reduced nuclear parafibromin expression in tumours supporting the pathogenic effects of these mutations.

CONCLUSIONS

This study supplies information on mutations and phenotypes of HPT-JT/FIHP syndrome in Chinese. Screening for gross deletion and point mutations of the CDC73 gene is necessary in susceptible subjects.

Parathyroid cancer and the CDC73 tumor suppressor gene

Parathyroid carcinoma (PC) is a rare endocrine neoplasm, usually causing severe primary hyperparathyroidism, that frequently causes death from unmanageable hypercalcemia. PC is frequently associated with somatic inactivating mutations of the CDC73 gene (previously called HRPT2), a gene discovered in association with the familial hyperparathyroidism-jaw tumor syndrome. DNA analysis for CDC73 mutation should be performed on all patients with seemingly sporadic PC since some 25% will carry a germline mutation. It is often difficult to make a firm diagnosis of PC by histopathology alone. That diagnosis often depends on the presence of local tissue invasion or distant metastases. If PC is suspected, en bloc resection at initial surgery is recommended. Medical therapy with cinacalcet, bisphosphonates or denosumab may temporarily ameliorate the hypercalcemia of inoperable PC.

Genetic and epigenetic changes in sporadic endocrine tumors: parathyroid tumors

Parathyroid neoplasia is most commonly due to benign parathyroid adenoma but rarely can be caused by malignant parathyroid carcinoma. Evidence suggests that parathyroid carcinomas rarely, if ever, evolve through an identifiable benign intermediate, with the notable exception of carcinomas associated with the familial hyperparathyroidism-jaw tumor syndrome. Several genes have been directly implicated in the pathogenesis of typical sporadic parathyroid adenoma; somatic mutations in the MEN1 tumor suppressor gene are the most frequent finding, and alterations in the cyclin D1/PRAD1 oncogene are also firmly established molecular drivers of sporadic adenomas. In addition, good evidence supports mutation in the CDKN1B/p27 cyclin-dependent kinase inhibitor (CDKI) gene, and in other CDKI genes as contributing to disease pathogenesis in this context. Somatic defects in additional genes, including β-catenin, POT1 and EZH2 may contribute to parathyroid adenoma formation but, for most, their ability to drive parathyroid tumorigenesis remains to be demonstrated experimentally. Further, genetic predisposition to sporadic presentations of parathyroid adenoma appears be conferred by rare, and probably low-penetrance, germline variants in CDKI genes and, perhaps, in other genes such as CASR and AIP. The HRPT2 tumor suppressor gene is commonly mutated in parathyroid carcinoma.

Understanding the genetic basis of parathyroid carcinoma

Parathyroid carcinoma has always been difficult to diagnose pathologically. In fact, most parathyroid tumors which are classified as carcinoma do not recur after excision, and most parathyroid tumors which actually metastasize or recur repeatedly in the neck are not recognized as malignant at first presentation. In 2002, germline HRPT2 (also known as CDC73) mutation was reported as the cause of hyperparathyroidism-jaw tumor (HPT-JT) syndrome, an autosomal dominant hereditary tumor syndrome associated with a lifetime risk of parathyroid carcinoma approaching 15 %. Subsequently, bi-allelic inactivation or mutation of HRPT2 has been reported in the majority of parathyroid carcinomas that actually behave in a malignant manner but very rarely in sporadic benign parathyroid disease. Furthermore, germline testing for HRPT2 mutation in patients presenting with parathyroid carcinoma often identifies occult HPT-JT syndrome even in the absence of a family history or other syndromic manifestations. HRPT2 mutation testing is not readily available, and loss of expression of parafibromin (the protein encoded by HRPT2) as determined by immunohistochemistry has been used as a surrogate marker of HRPT2 mutation. Immunohistochemistry for parafibromin can be technically difficult and has been deployed by different investigators with variable enthusiasm and success. However, proponents have found immunohistochemistry for parafibromin useful to definitively confirm a pathological diagnosis of parathyroid carcinoma, predict a worse outcome in definite parathyroid carcinomas, triage formal genetic testing for HPT-JT syndrome, and predict the outcome of histologically atypical parathyroid adenomas.

CDC73 mutational status and loss of parafibromin in the outcome of parathyroid cancer

Inactivating mutations of the CDC73 tumor suppressor gene have been reported in parathyroid carcinomas (PC), in association with the loss of nuclear expression of the encoded protein, parafibromin. The aim of this study was to further investigate the role of the CDC73 gene in PC and evaluate whether gene carrier status and/or the loss of parafibromin staining might have an effect on the outcome of the disease. We performed genetic and immunohistochemical studies in parathyroid tumor samples from 35 patients with sporadic PC. Nonsense or frameshift CDC73 mutations were detected in 13 samples suitable for DNA sequencing. Six of these mutations were germline. Loss of parafibromin expression was found in 17 samples. The presence of the CDC73 mutation as well as the loss of parafibromin predicted a high likelihood of subsequent recurrence and/or metastasis (92.3%, P=0.049 and 94.1%, P=0.0017 respectively), but only the latter was associated with a decreased overall 5- and 10-year survival rates (59%, P=0.107, and 23%, P=0.0026 respectively). The presence of both the CDC73 mutation and loss of parafibromin staining compared with their absence predicted a lower overall survival at 10- (18 vs 84%, P=0.016) but not at 5-year follow-up. In conclusion, loss of parafibromin staining, better than CDC73 mutation, predicts the clinical outcome and mortality rate. The added value of CDC73 mutational analysis is the possibility of identifying germline mutations, which will prompt the screening of other family members.

Negative parafibromin staining predicts malignant behavior in atypical parathyroid adenomas

BACKGROUND

The histopathological criteria for carcinoma proposed by the World Health Organization (WHO) are imperfect predictors of the malignant potential of parathyroid tumors. Negative parafibromin (PF) and positive protein gene product 9.5 (PGP9.5) staining are markers of CDC73 mutation and occur commonly in carcinoma but rarely in adenomas. We investigated whether PF and PGP9.5 staining could be used to predict the behavior of atypical parathyroid adenomas--tumors with atypical features that do not fulfill WHO criteria for malignancy.

METHODS

Long-term outcomes were compared across four groups: group A, WHO-positive criteria/PF-negative staining; group B, WHO(+)/PF(+), group C; WHO(-)/PF(-); and group D, WHO(-)/PF(+).

RESULTS

Eighty-one patients were included in the period 1999-2012: group A (n = 13), group B (n = 14), group C (n = 21), and group D (n = 33). Mortality and recurrence rates, respectively, for group A were 15 and 38%, for group B 7 and 36%, for group C 0 and 10%, and for group D 0 and 0%. The PGP9.5(+) ratios for groups A to D were 85, 78, 71, and 12%, further informing prognosis. Five-year disease-free survival for groups A to D were 55, 80, 78, and 100%, respectively. Tumor recurrence was significantly associated with PF (p = 0.048) and PGP9.5 (p = 0.003) staining.

CONCLUSIONS

Although WHO criteria are essential to differentiate parathyroid carcinoma from benign tumors, the presence of negative PF staining in an atypical adenoma predicts outcome better, whereas PF-positive atypical adenomas do not recur and can be considered benign. PF-negative atypical adenomas have a low but real recurrence risk and should be considered tumors of low malignant potential.

The Utility of Immunohistochemistry for Providing Genetic Information on Tumors

With advances in immunohistochemical technology and growing knowledge of the molecular genetics of tumors, immunohistochemistry is playing an increasingly important role in providing genetic information for tumors. Specific chromosomal translocations can be demonstrated through detection of the protein product of one of the genes involved in gene fusion (such as BCL2, cyclin D, and ALK). Some mutations can be detected by (1) aberrant localization of the protein product (such as β-catenin and nucleophosmin), (2) abnormal accumulation of the protein product as a result of stabilization of the protein (such as p53), and (3) mutation-specific antibodies directed against the mutant protein (such as isocitrate dehydrogenase gene R132H mutation, epidermal growth factor receptor gene L858R and exon 19 deletion mutations, and BRAF gene V600E mutation). Gene deletion or loss of function can be demonstrated by the loss of immunostaining for the protein product (such as mismatch repair proteins in microsatellite-unstable tumors, E-cadherin in lobular carcinoma of the breast, and INI1 in rhabdoid tumors, atypical teratoid/rhabdoid tumors, and epithelioid sarcomas). Gene amplification can be demonstrated by overexpression of the protein product (such as HER2 in breast and gastric cancers, and MDM2 or CDK4 in well-differentiated/dedifferentiated liposarcomas). Viruses associated with tumors can be demonstrated directly (such as Epstein-Barr virus latent membrane protein-1 in Hodgkin lymphomas, human herpesvirus 8 in Kaposi sarcomas, and Merkel cell polyomavirus in Merkel cell carcinomas) or by a surrogate marker (such as p16 in human papillomavirus infection). In this review, examples are given to illustrate the principles and pitfalls of these applications.

Molecular diagnosis of primary hyperparathyroidism in familial cancer syndromes

In the last few years, causative genes have been identified for most of the familial hyperparathyroidism conditions. Germline mutations in the tumour suppressors multiple endocrine neoplasia type 1 (MEN1) and hyperparathyroidism 2 (HRPT2) provide a molecular diagnosis of multiple endocrine neoplasia type 1 and hyperparathyroidism jaw tumour syndrome, respectively. Germline mutations in the proto-oncogene RET (rearranged during transfection) provide a molecular diagnosis of multiple endocrine neoplasia type 2. Germline mutations of both MEN1 and, less frequently HRPT2, have been found in familial isolated hyperparathyroidism. A molecular diagnosis can now be incorporated into the management of patients with these conditions, however, the ease of diagnostics and value of genetic information in the context of clinical screening and early surgical intervention varies between these disorders. This review focuses on familial hyperparathyroidism and its known causative genes in the setting of neoplastic syndromes, with particular discussion of recent developments in the molecular diagnosis of parathyroid carcinoma.

Biomarkers of parathyroid carcinoma

The diagnosis of parathyroid carcinoma can be challenging, and adjuvant therapies such as radiotherapy and chemotherapy are not particularly beneficial in the management of this disease, creating a challenge when dealing with unresectable recurrent and metastatic malignancy. We investigated the expression profile of biomarkers that represent potential markers of malignancy or targets for novel therapies in this disease. We constructed a tissue microarray of parathyroid carcinomas from 10 patients as well as parathyroid adenomas from 25 patients and stained the slides for 34 proteins involved in angiogenesis (platelet-derived growth factor receptor (PDGFR)-α, PDGFR-β, vascular endothelial growth factor receptor-2 (VEGFR-2), and epidermal growth factor receptor (EGFR)), inflammation (cyclooxygenase (COX)-1 and COX-2), cell adhesion (matrix metalloproteinase (MMP)-1, CD9, and keratin 7), cell cycle (Cdc2p34, cyclin D1, retinoblastoma (Rb), p27, p21, parafibromin, Bmi-1, 14-3-3σ, and p53), and apoptosis (Bcl-2a, Mcl-1, Bcl-xL, and glutathione-S-transferase-isoenzyme π (Gst-π)) along with some markers of the sonic hedgehog (Smo, SHH, Gli-1, Gli-2, Gli-3, and patched), mTOR (AKT, mammalian target of rapamycin (mTOR), and Forkhead box O (FoxO)-1), and WNT (Wisp-1, Wisp-2, and β-catenin) signal transduction pathways. Protein expression was determined using computerized image analysis software (Spectrum Plus©, Aperio). Bcl-2a, parafibromin, Rb, and p27 were significantly decreased to variable degrees in all parathyroid carcinomas. COX-1/2, CD9, MMP-1, FoxO-1, VEGFR-2, PDGFR-α/β, Gst-π, Gli-1, Gli-2, Gli-3, and patched were expressed in the majority of benign and malignant tumor cells. These results indicate that the use of a panel that includes Bcl-2a, parafibromin, Rb, and p27 may be helpful in the assessment of atypical parathyroid neoplasms. Although the majority of other markers studied are also expressed in both benign and malignant parathyroid neoplasms, we have identified several potentially important target proteins related to angiogenesis and cell proliferation along with COX-1/2, Gst-π and members of sonic hedgehog pathway that may be therapeutic targets in parathyroid carcinoma. While these results are preliminary, a successful outcome of a clinical trial directed against these novel targets would provide much needed systemic adjuvant treatment for patients with metastatic parathyroid carcinoma.

Expression of parafibromin in major renal cell tumors

Parafibromin, encoded by HRPT2 gene, is a recently identified tumor suppressor. Complete and partial loss of its expression have been observed in hyperparathyroidism-jaw tumor (HPT-JT), parathyroid carcinoma, breast carcinoma, lung carcinoma, gastric and colorectal carcinoma. However, little has been known about its expression in renal tumors. In order to study the expression of parafibromin in a series of the 4 major renal cell tumors - clear cell renal cell carcinoma (ccRCC), papillary renal cell carcinoma (pRCC), chromophobe renal cell carcinoma (chRCC) and oncocytoma, one hundred thirty nine renal tumors including 61 ccRCCs, 37 pRCCs, 22 chRCCs and 19 oncocytomas were retrieved and used for the construction of renal tissue microarrays (TMAs). The expression of parafibromin was detected by immunohistochemical method on the constructed TMAs. Positive parafibromin stains are seen in 4 out of 61 ccRCCs (7%), 7 out of 37 pRCCs (19%), 12 out of 23 chRCCs (52%) and all 19 oncocytomas (100%). Parafibromin expression varies significantly (P<8.8×10⁻¹⁶) among the four major renal cell tumors and were correlated closely with tumor types. No correlation of parafibromin expression with tumor staging in ccRCCs, pRCCs and chRCCs, and Fuhrman nuclear grading in ccRCCs and pRCCs was seen. In summary, parafibromin expression was strongly correlated with tumor types, which may suggest that it plays a role in the tumorigenesis in renal cell tumors.

Genome-wide and locus specific alterations in CDC73/HRPT2-mutated parathyroid tumors

Mutations in the hyperparathyroidism type 2 (HRPT2/CDC73) gene and alterations in the parafibromin protein have been established in the majority of parathyroid carcinomas and in subsets of parathyroid adenomas. While it is known that CDC73-mutated parathyroid tumors display specific gene expression changes compared to CDC73 wild-type cases, the molecular cytogenetic profile in CDC73-mutated cases compared to unselected adenomas (with an expected very low frequency of CDC73 mutations) remains unknown. For this purpose, nine parathyroid tumors with established CDC73 gene inactivating mutations (three carcinomas, one atypical adenoma and five adenomas) were analyzed for copy number alterations and loss of heterozygosity using array-comparative genomic hybridization (a-CGH) and single nucleotide polymorphism (SNP) microarrays, respectively. Furthermore, CDC73 gene promoter methylation levels were assessed using bisulfite Pyrosequencing. The panel included seven tumors with single mutation and three with double mutations of the CDC73 gene. The carcinomas displayed copy number alterations in agreement with previous studies, whereas the CDC73-mutated adenomas did not display the same pattern of alterations at loci frequently deleted in unselected parathyroid tumors. Furthermore, gross losses of chromosomal material at 1p and 13 were significantly (p = 0.012) associated with parathyroid carcinomas as opposed to adenomas. Quantitative PCR-based copy number loss regarding CDC73 was observed in three adenomas, while all the carcinomas were diploid or showed copy number gain for CDC73 gene. Hypermethylation of the CDC73 gene promoter was not observed. Our data could suggest that CDC73-mutated parathyroid adenomas exhibit a partly unique cytogenetic profile in addition to that of carcinomas and unselected adenomas. Furthermore, CDC73-mutated carcinomas displayed losses at 1p and 13 which are not seen in CDC73-mutated adenomas, making these regions of interest for further studies regarding malignant properties in tumors from CDC73-mutated cases. However, due to the small sample size, validation of the results in a larger cohort is warranted.

Novel HRPT2/CDC73 gene mutations and loss of expression of parafibromin in Chinese patients with clinically sporadic parathyroid carcinomas

OBJECTIVE

It is widely recognized that the diagnosis of parathyroid carcinoma (PC) is often difficult because of the overlap of characteristics between malignant and benign parathyroid tumors, especially at an early stage. Based on the identification of tumor suppressor gene HRPT2/CDC73 and its association with hereditary and sporadic PC, screening of gene mutations and detection of parafibromin immunoreactivity have been suggested as diagnostic instruments of PC in Whites. There is little information about HRPT2/CDC73 mutations and its corresponding protein expression in patients with sporadic PC in Chinese population, and the long-term follow-up data is scarce.

METHODS

Paraffin-embedded tissues were obtained from 13 patients with PC, 13 patients with parathyroid adenoma (PA) and 7 patients with parathyroid hyperplasia(PH), and 6 normal parathyroid (NP) tissues as controls. Peripheral blood from 11 patients with PC was collected. PCR products using Genomic DNA extracted from tumor tissues or blood as template was sequenced for HRPT2/CDC73 gene. Expression of parafibromin in tumor tissues was evaluated by immunohistochemical analysis.

RESULTS

Six mutations in 6 of 13 patients with PC were identified, with three being novel. Four of them were germ-line mutations. Patients with mutations were susceptible to recurrence of the PC. Complete (8/13, 61.5%) or partial (5/13, 38.5%) loss of parafibromin expression was observed in PC tissues. All of tissue samples from normal parathyroid or benign parathyroid tumors displayed positive immunostaining of parafibromin except one adenoma.

CONCLUSIONS

The present study supplies information on the mutations and protein expression of HRPT2/CDC73 gene and phenotypes of parathyroid carcinoma in Chinese population. And the expanded mutation database of this gene may benefit patients in the diagnosis and treatment of this disease.

CDC73 mutations and parafibromin immunohistochemistry in parathyroid tumors: clinical correlations in a single-centre patient cohort

OBJECTIVE

To determine if molecular and immunohistochemical (IHC) features of the HRPT2/CDC73 gene and its product, parafibromin, predict the natural history of parathyroid malignancy, particularly atypical adenoma, as seen in a single-centre patient cohort.

METHODS

Matched tumor and non-tumor tissues were obtained from 46 patients with parathyroid carcinoma (CA) (n = 15), atypical adenoma (AA) (n = 14) and typical adenoma (TA) (n = 17), as defined by standardized histopathological criteria. Exons and exon-intron boundaries of the CDC73 gene were sequenced to identify germline or somatic mutations. IHC staining for parafibromin was performed and scored as positive if nuclear staining was at least partially IHC-positive.

RESULTS

Mutations of CDC73 were observed in 9/15 (60 %) CA, 2/14 (14 %) AA, and 1/17 (6 %) TA tumors. A recurrent two basepair mutation in exon 7 -- c.679_680delAG -- accounted for half of all identified mutations. Absence of parafibromin nuclear staining was noted in 8/12 (67 %) CA, 2/13 (15 %) AA, and 3/17 (18 %) TA tumors. Median follow up times were 88 months for CA, 76 months for AA, and 104 months for TA patients. One patient, a member of a previously reported multiplex family with a germline CDC73 mutation was found to have a second adenoma after removal of an atypical adenoma.

CONCLUSIONS

Molecular screening and IHC are both useful tools in the differential diagnosis of parathyroid tumors, but both have limited sensitivity and specificity. CDC73 mutations and negative immunostaining were common in atypical adenomas, but no local recurrence was observed in any case with successful surgical removal after follow-up periods of 27 to 210 months.

Metastatic parathyroid carcinoma initially misdiagnosed as parathyroid adenoma: the role of parafibromin in increasing diagnostic accuracy

Parathyroid carcinoma, although a rare cause of primary hyperparathyroidism, carries a significant morbidity and mortality from severe symptomatic hypercalcaemia and related complications. We report a case where the diagnosis was not considered from the outset and review the current clinical and histopathological markers available to assist in the diagnosis of parathyroid carcinoma.

Genetic characterization of large parathyroid adenomas

In this study, we genetically characterized parathyroid adenomas with large glandular weights, for which independent observations suggest pronounced clinical manifestations. Large parathyroid adenomas (LPTAs) were defined as the 5% largest sporadic parathyroid adenomas identified among the 590 cases operated in our institution during 2005-2009. The LPTA group showed a higher relative number of male cases and significantly higher levels of total plasma and ionized serum calcium (P<0.001). Further analysis of 21 LPTAs revealed low MIB1 proliferation index (0.1-1.5%), MEN1 mutations in five cases, and one HRPT2 (CDC73) mutation. Total or partial loss of parafibromin expression was observed in ten tumors, two of which also showed loss of APC expression. Using array CGH, we demonstrated recurrent copy number alterations most frequently involving loss in 1p (29%), gain in 5 (38%), and loss in 11q (33%). Totally, 21 minimal overlapping regions were defined for losses in 1p, 7q, 9p, 11, and 15q and gains in 3q, 5, 7p, 8p, 16q, 17p, and 19q. In addition, 12 tumors showed gross alterations of entire or almost entire chromosomes most frequently gain of 5 and loss of chromosome 11. While gain of 5 was the most frequent alteration observed in LPTAs, it was only detected in a small proportion (4/58 cases, 7%) of parathyroid adenomas. A significant positive correlation was observed between parathyroid hormone level and total copy number gain (r=0.48, P=0.031). These results support that LPTAs represent a group of patients with pronounced parathyroid hyperfunction and associated with specific genomic features.

Familial hyperparathyroidism due to a germline mutation of the CDC73 gene: implications for management and age-appropriate testing of relatives at risk

OBJECTIVE

To discuss the implications of a young age at diagnosis in a family member with hyperparathyroidism-jaw tumor syndrome, the youngest published case to date, due to a mutation of the CDC73 gene (formerly known as HRPT2); to review this family with regard to modifications of guidelines for surveillance of hyperparathyroidism and other associated features in affected and at-risk relatives; and to discuss surgical recommendations in this syndrome.

METHODS

A review of English-language publications in PubMed and a review of GeneReviews were conducted pertaining to the subject of familial hyperparathyroidism. A case is described, and the family pedigree is discussed.

RESULTS

Review of the literature revealed that CDC73-related disorder has not previously been reported in patients younger than 10 years. This finding has been the basis for the recommendation for initiation of surveillance for disease manifestations at that age. Review of the family history of our current patient revealed a 7-year-old nephew with hypercalcemia attributable to primary hyperparathyroidism.

CONCLUSION

Surveillance of hyperparathyroidism in affected persons and genetic testing of relatives at risk are currently recommended to start at 10 years of age. We recommend that these be conducted at a younger age, preferably 5 to 10 years before the earliest diagnosis of hyperparathyroidism within the family, and potentially at birth in families with a known mutation of the CDC73 gene, in light of the malignant potential of the disease.

Molecular diagnosis of parathyroid carcinoma: a reality in the near future

INTRODUCTION

Parathyroid carcinoma (PC) is a rare endocrine malignancy that still suffers from a problem of delayed clinical diagnosis. Consequently, it usually is not recognized preoperatively and often is not conclusively identified during the operation either.

AREAS COVERED

The role played by parafibromin in the development of PC, representing an important advance in understanding the pathogenesis of this malignancy, is discussed. Through a careful search of the international literature, using "parathyroid carcinoma", "molecular genetics of parathyroid carcinoma" and "parathyroid tumorigenesis" as key words, other less mentioned molecular mechanisms are reappraised as potential molecular markers of PC; we also discuss their potential role in 20 parathyroid outgrowths. Finally, both the major efforts and the limitations of reported molecular diagnostic techniques and diagnostic markers are considered.

EXPERT OPINION

Currently, several critical issues still need to be addressed, such as the lack of: i) common criteria for the histopathological diagnosis of parathyroid malignancy and ii) timely appropriated preoperative diagnosis of PC. The latter issue would be of fundamental importance to assist the surgeon in performing a complete resection of all carcinomatous tissue at the time of the initial surgery, allowing for the greatest likelihood of a cure.

The tumor suppressor CDC73 interacts with the ring finger proteins RNF20 and RNF40 and is required for the maintenance of histone 2B monoubiquitination

Monoubiquitination of histone H2B is a dynamic post-translational histone modification associated with transcriptional elongation and the DNA damage response. To date, dysregulation of histone monoubiquitination has not been linked to pathogenic mutations in genes encoding proteins, or co-factors, catalyzing this modification. The tumor suppressor cell division cycle 73 (CDC73) is mutated and/or down-regulated in parathyroid carcinoma, renal, breast, gastric and colorectal tumors, as well as in the germline of patients with the familial disorder-hyperparathyroidism jaw tumor syndrome. Using CDC73 as bait in a yeast two-hybrid assay, we identified the ring finger proteins RNF20 and RNF40 as binding partners of this tumor suppressor. These polypeptides constitute a heterodimeric complex that functions as the E3 ubiquitin ligase for monoubiquitination of histone H2B at lysine 120 (H2B-K120). We show that RNF20 and RNF40 bind to discrete, but closely located, residues on CDC73. Monoubiquitinated H2B-K120 was significantly reduced after loss of nuclear CDC73, both in vitro upon down-regulation of CDC73, and in CDC73 mutant parathyroid tumors. A second histone modification, trimethylation of histone 3 at lysine 4 (H3-K4me3), remained unchanged in the presence of mutant or down-regulated CDC73, suggesting that H3-K4me3 is not always tightly linked to H2B-K120 monoubiquitination for transcription as previously described. This is the first report of pathogenic mutations affecting histone monoubiquitination. We conclude that CDC73 is required for the maintenance of H2B-K120 monoubiquitination and propose that reduction in levels of monoubiquitinated H2B-K120 is a major mechanism whereby mutations in CDC73 exert their tumorigenic effect.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

CDC73-related hereditary hyperparathyroidism: five new mutations and the clinical spectrum

OBJECTIVE

Hyperparathyroidism-jaw tumour (HPT-JT) syndrome is a rare autosomal dominant cause of benign and malignant parathyroid tumours, ossifying jaw tumours, various cystic and neoplastic renal abnormalities and benign and malignant uterine tumours. Disease-causing mutations have been localised in the tumour suppressor gene CDC73. There is limited information available on the mutations, and resulting phenotypes and long-term follow-up data are especially scarce.

DESIGN

We analysed the clinical data from 16 patients (including three families) carrying mutations in the CDC73 gene. We describe five new mutations/gene variants, the corresponding phenotypes of these carriers and the long-term follow-up.

METHODS

The 16 patients were evaluated at an endocrine outpatient clinic and at a surgical department. DNA samples were obtained for sequence analysis of the CDC73 gene.

RESULTS

Clinical features of HPT-JT syndrome were detected in 13 of the 15 carriers with germline CDC73 mutations. The major features were benign (n=7; 47%) or cancerous (n=3; 20%) HPT-JT was present in eight cases (53%). Most patients had severe hypercalcaemia, and median serum calcium levels were 3.36 mmol/l. A patient with non-secretory parathyroid carcinoma was included. HPT was diagnosed at a median age of 28.5 years. Mutational analysis of the CDC73 gene identified eight sequence changes, three of them have been reported previously, whereas five are novel: c.1346delG, c.88_94delTTCTCCT, the non-coding variants, c.307+5G>T and c.424-5T>C and c.*12C>A of unknown significance.

CONCLUSIONS

This study significantly increases the information available on the mutations and phenotypes of HPT-JT syndrome.

Detection of the first gross CDC73 germline deletion in an HPT-JT syndrome family

Hereditary primary hyperparathyroidism (HPT) may develop as a solitary endocrinopathy (FIHP) or as part of multiple endocrine neoplasia Type 1, multiple endocrine neoplasia Type 2A, or hereditary HPT-jaw tumor syndrome. Inactivating germline mutations of the tumor suppressor gene CDC73 account for 14 and 50% of all FIHP and HPT-JT patients, respectively, and have also been found in almost 20% of apparently sporadic parathyroid carcinoma patients. Although more than 60 independent germline mutations have been described, to date no rearrangement affecting the CDC73 locus has been identified. By means of multiplex-PCR we found a large germline deletion affecting the whole gene in a two-generation HPT-JT family. Subsequently array-CGH and specific PCR analysis determined that the mutation spanned ∼ 547 kb, and included four additional genes: TROVE2, GLRX2, B3GALT2, and UCHL5. Although no clear mutation-specific phenotype was found associated to the presence of the mutation, further studies are needed to assess whether the loss of the neighboring genes could modify the phenotype of carriers. There was complete absence of nuclear staining in the two HPT-JT-related tumors available. The finding of the first rearrangement affecting the CDC73 gene warrants screening for this tumor suppressor gene inactivation mechanism not only in high-risk CDC73 point mutation-negative HPT-JT families, but also in FIHP patients.

Parafibromin immunohistochemical staining to differentiate parathyroid carcinoma from parathyroid adenoma

BACKGROUND

Parafibromin is a protein encoded by the HRPT2 oncosuppressor gene, and the expression is reported to be decreased or absent in parathyroid carcinomas.

METHODS

A total of 26 tumor specimens from 18 patients with adenoma and 8 patients with carcinoma were immune-stained with an antibody against parafibromin.

RESULTS

Parafibromin immunostaining showed strong positivity in 17 of 18 adenomas. Negative staining was noted in 3 of 8 carcinomas, and weak positivity was found in 3 of 8 carcinomas. The remaining 2 cases of carcinoma showed strong positivity. The loss of parafibromin expression (negative or weak positivity) demonstrated 94.4% specificity in the diagnosis of parathyroid carcinomas. Relapses or distant metastases of carcinoma occurred only in cases in which there was a loss of parafibromin immunostaining.

CONCLUSIONS

Loss of parafibromin immunostating showed promising results in the differential diagnosis of parathyroid carcinoma from adenoma and may also serve as a prognostic marker.

Parathyroid cancer

OBJECTIVE

To review the current knowledge pertaining to the etiology, molecular pathogenesis, and management of parathyroid carcinoma, a rare presentation of primary hyperparathyroidism.

METHODS

The existing MEDLINE English-language literature was reviewed using the search terms "parathyroid" and "carcinoma" or "cancer."

RESULTS

Parathyroid cancer is a rare endocrine tumor accounting for a small proportion of cases of primary hyperparathyroidism. Recent database studies indicate increasing incidence rates. Its etiology is unknown, although numerous molecular alterations have been described, and the tumors also occur in association with germline mutations in the CDC73 gene. Most affected patients present with severe hypercalcemia; however, the diagnosis can be challenging. Complete surgical resection remains the mainstay of treatment and provides the best chance of cure, although data from small series suggest that external beam radiation may also reduce the high recurrence rates. No effective chemotherapy regimens are currently available. A significant number of patients develop recurrent disease and need additional procedures; however, long-term survival is possible with palliative surgery. Medical management of chronic and debilitating hypercalcemia with calcimimetics is often necessary and is an important adjunct in patients with recurrent and metastatic disease.

CONCLUSIONS

Further elucidation of the molecular pathogenesis of parathyroid carcinomas will enhance our understanding of etiology and behavior of this uncommon entity. Future research must be directed at identifying more effective therapies for this condition.

Downregulation of CASR expression and global loss of parafibromin staining are strong negative determinants of prognosis in parathyroid carcinoma

Parathyroid carcinoma is associated with mutations in the HRPT2/CDC73 gene and with decreased parafibromin and calcium-sensing receptor (CASR) expression, but in some cases establishing an unequivocal diagnosis remains a challenge. The aim of our study was to evaluate the prognostic value of CASR and parafibromin expression and of HRPT2/CDC73 mutations in patients with an established diagnosis of parathyroid carcinoma. Data on survival and disease-free survival were obtained from hospital records of 23 patients with an established diagnosis of parathyroid carcinoma in whom CASR and parafibromin expression and HRPT2/CDC73 mutation analyses were available from paraffin-embedded pathological specimens. Kaplan-Meier curves were used for survival analysis. Downregulation of CASR expression, global loss of parafibromin staining and a HRPT2/CDC73 mutation were, respectively, found in 7 (30%), 13 (59%) and 4 (17%) patients, and were associated with, respectively, 16-fold, 4-fold and 7-fold increased risk of developing local or distant metastasis. These findings suggest that although downregulation of CASR expression, global loss of parafibromin staining and mutations in the HRPT2/CDC73 gene are tools of proven value to assist in establishing a diagnosis of parathyroid carcinoma, their absence does not exclude it. Notwithstanding, we demonstrate a significant added value of these markers as strong determinants of increased malignant potential and thus as negative prognostic markers in this malignancy.

Parathyroid tumors and related disorders

Primary hyperparathyroidism (P-HPT) is a common endocrine disorder that occurs as a result of adenomas (80-85%), hyperplasias (10-15%) or carcinomas (<1%) of the parathyroid glands. Molecular genetic analyses of heritable P-HPT syndromes have provided considerable insight into the understanding of sporadic parathyroid tumors and hyperplasias. This review will focus on the criteria for classification of parathyroid proliferative disorders and will highlight our understanding of these lesions at the molecular level. Advances in radiological imaging techniques together with the rapid intraoperative parathyroid hormone assay will be reviewed with respect to current treatment approaches for P-HPT.

Identification of de novo germline mutations in the HRPT2 gene in two apparently sporadic cases with challenging parathyroid tumor diagnoses

The diagnosis of parathyroid carcinomas is often difficult. HRPT2 mutations have been identified in familial [hyperparathyroidism-jaw tumor (HPT-JT) syndrome] and sporadic parathyroid carcinomas, supporting that HRPT2 mutations may confer a malignant potential to parathyroid tumors. In this study, we report the clinical, histopathological, and genetic investigation of two unrelated cases, whom had apparently sporadic malignant parathyroid tumors, initially diagnosed as adenomas. In one case, the differential diagnosis was complicated by cervical seeding of parathyroid tumor cells. Genetic studies identified de novo HRPT2 germline mutations in cases 1 (c.518_521delTGTC [p.Ser174LysfsX27]) and 2 (c.226 C > T [p.Arg76X]), unveiling the hereditary HPT-JT syndrome in both patients. Furthermore, the identification of somatic mutations in the patients‟ parathyroid tumors provided evidence for complete inactivation of the HRPT2 gene, which was consistent with the tumor malignant features. The sensitivity of parafibromin immunostaining to detect HRPT2 mutations was limited. The present data suggests that patients with apparently sporadic parathyroid carcinomas, or parathyroid tumors with atypical histological features, should undergo molecular genetic testing, as it may detect germline HRPT2 mutations. Establishing the diagnosis of hereditary HPT-JT syndrome is relevant for clinical counseling and management of the carriers and their relatives.

Parathyroid carcinoma arising from four-gland hyperplasia

OBJECTIVE

To report the use of immunohistochemical staining for parafibromin, APC, and galectin-3 to evaluate the malignant potential of a resected parathyroid specimen in a patient initially presenting with primary hyperparathyroidism attributable to 4-gland hyperplasia, who subsequently developed metastatic parathyroid carcinoma.

METHODS

We describe a patient with primary hyperparathyroidism who underwent a 3-gland resection of hypercellular parathyroid glands, with postoperative normalization of her serum calcium and parathyroid hormone levels. She returned 4 years later with recurrent hypercalcemia and underwent partial resection of her remaining hypercellular parathyroid gland, without improvement of her hypercalcemia. Selective venous sampling localized the source as draining into her azygos vein, and metastatic parathyroid carcinoma was ultimately diagnosed.

RESULTS

Immunohistochemical staining for parafibromin, APC, and galectin-3 suggested the malignant potential of the atypical adenoma removed during the patient's original operation, which is believed to be the source of her metastatic disease. Access to this information by the treating surgeon may have prompted a more extensive en bloc resection or more vigilant follow-up that could have altered the patient's clinical course.

CONCLUSION

Immunohistochemical staining for parafibromin, APC, and galectin-3 can be used to help distinguish the source of metastatic disease in patients with parathyroid carcinoma. Selective venous sampling may help localize metastatic parathyroid carcinoma when the source is otherwise not apparent.

Parafibromin expression is an independent prognostic factor for colorectal carcinomas

Parafibromin is a protein encoded by hyperparathyroidism 2, and its down-regulated expression is involved in the pathogenesis of parathyroid, breast, and gastric carcinomas. This study aimed to clarify the roles of parafibromin expression in tumorigenesis, progression, and prognosis of colorectal carcinomas. Parafibromin-expressing plasmid was transfected into DLD-1 cells with the phenotypes, and related molecules were examined. Parafibromin expression was examined in colorectal samples by immunohistochemistry, in situ hybridization, Western blot, or reverse transcription polymerase chain reaction. It was found that parafibromin overexpression could cause G1 arrest and enhance differentiation of DLD-1 cells. There was a high expression of p21, p27, and cyclin E, but low expression of cyclin D1 messenger RNA, phospho-cdc2, and phospho-cdc25c proteins. Parafibromin could inhibit c-myc messenger RNA expression by binding to c-myc promoter. Expression levels of nuclear parafibromin and parafibromin messenger RNA were decreased from colorectal nonneoplastic mucosa and adenomas to carcinomas (P < .05). Immunohistochemically, parafibromin expression was inversely correlated with tumor size, depth of invasion, lymph node metastasis, clinicopathologic staging, and poor prognosis of carcinomas (P < .05). It was suggested that parafibromin overexpression might suppress cell cycle progression and promote differentiation of DLD-1 cells. Aberrant parafibromin expression possibly contributes to the pathogenesis, growth, invasion, and metastasis of colorectal carcinomas and could be regarded as an independent factor to indicate a favorable prognosis for patients with colorectal carcinomas.