p16iNK4a as a complementary marker of high-grade intraepithelial lesions of the uterine cervix. I: Experience with squamous lesions in 189 consecutive cervical biopsies

Diagnostic utility of p16INK4a: a reappraisal of its use in cervical biopsies

p16(INK4a), an indirect marker of cell cycle dysregulation, is commonly expressed in cervical dysplasias and carcinomas associated with high risk human papillomavirus (HR-HPV) infections. Although p16(INK4a) immunohistology is routinely used as a cost effective surrogate marker, many of the published articles are confusing and contradictory. The discrepancies can be ascribed to a multitude of factors operating at the molecular, technical and interpretative levels. In the first place, our simplistic model of viral mediated oncogenesis is speculative and fails to account for all the known biomolecular changes. Unresolved technical issues include the variables of tissue fixation, antibody dilution, antibody isotype and clone, and the sensitivity of the particular detection method. Within any controlled staining method, strong diffuse or 'block' immunoreactivity in squamous cells may be found in moderate/severe dysplasia (CIN 2/3) and invasive squamous carcinoma. In contrast, focal or multifocal reactivity in squamous cells may be artefactual, related to low risk or HR-HPV. p16(INK4a) is less reliable when dealing with glandular lesions since considerable overlap exists between reactive and dysplastic lesions. In addition not all glandular dysplasias/carcinomas are HR-HPV related, nor are all p16(INK4a) immunoreactive lesions associated with HR-HPV. We conclude that p16(INK4a) immunoperoxidase shows greater specificity than sensitivity for squamous lesions; in comparison, glandular dysplasias/carcinomas show reduced specificity and sensitivity. Like all cell cycle regulatory proteins, the future diagnostic role of p16(INK4a) is limited. The ideal diagnostic molecular test for cervical dysplasias will detect a HR-HPV related product after, but not before, cell transformation and will reliably predict those cases yet to experience disease progression.

Biomarkers in cervical precancer management: the new frontiers

The major cause of cervical cancer and its pre-invasive lesions is persistent infections with oncogenic human papillomavirus (HPV). Viral replication and integration in the cervix depends on the ordered expression of viral gene products, which can lead to overexpression of multiple molecular proteins or biomarkers. These novel biomarkers allow the monitoring of essential molecular events in histological or cytological specimens and are likely to improve the detection of lesions that have a high risk of progression in both primary screening and triage settings. This review focuses on these molecular markers and their role in the diagnosis and management of cervical dysplasia and cancer.

Coordinate expression of cytokeratin 8 and cytokeratin 17 immunohistochemical staining in cervical intraepithelial neoplasia and cervical squamous cell carcinoma: an immunohistochemical analysis and review of the literature

OBJECTIVE

Several Cytokeratin (CK) isoforms have been analyzed in cervical intraepithelial lesions. However, previously reported numbers of specimens have been too low to evaluate any correlation between CK and CIN.

METHODS

We examined the immunohistochemical staining of p16, CK8, and CK17 in 134 cervical tissues obtained by punch biopsy and graded as follows: CIN I (n=39), CIN II (n=31), CIN III (n=43), SCC (n=21).

RESULTS

p16 staining was identified in 74.4% of CIN I, 93.6% of CIN II, 97.7% of CIN III, and 100% of SCC cases. CK8 and CK17 staining were identified in 12.8% and 33.3% of CIN I, 22.6% and 58.1% of CIN II, 62.8% and 81.4% of CIN III, and 71.4% and 95.2% of SCC cases, respectively. Interestingly, positivity for CK8 and CK17 correlated with increasing lesion grade of the intraepithelial lesions and also correlated with p16 staining (p16, p=0.0008; CK8, p<0.0001, and CK17, p<0.0001), and a coordinate expression profile of CK8[+]/CK17[+] correlates with increasing CIN grade and carcinoma (likewise, a coordinate expression profile of CK8[-]/CK17[-] correlates with decreasing CIN grade and absence of carcinoma), but expression of just CK8 (CK8[+]/CK17[-]) or just CK17 (CK8[-]/CK17[+]) does not correlate with increasing CIN grade and carcinoma.

CONCLUSIONS

Results of the present study showed that p16, CK8, and CK17 immunostaining differed according to the degree of cervical intraepithelial lesions and SCC, and surprisingly, that staining was significantly correlated with increasing lesion grade of CIN and SCC.

Human papillomavirus (HPV) related carcinomas of the upper aerodigestive tract

Epidemiologic, clinical, morphologic and molecular evidence show that high risk HPV, particularly type 16, is a prerequisite for some carcinomas of the upper aerodigestive tract (UADT), particularly tonsil and base of tongue. Sexual transmission is an important mode of infection while tobacco use and excessive drinking are not considered risk factors. HPV + tumors are distinct clinically and pathologically. They are more common in young patients (<40 years) with a male to female ratio of 4:1. They usually present as a small or occult primary tumor with advanced neck disease. Microscopically they are non-keratinizing squamous cell carcinomas with basaloid features, excessive mitosis and comedo type necrosis. The tumors have a distinct immunohistochemical profile characterized by strong and diffuse p16 reactivity, low or negative p53 staining and high Ki67 labeling scores. HPV + carcinomas are more radio-sensitive and have a better prognosis than the classical keratinizing SCC of the UADT. An anti-HPV vaccine has recently been made available for prevention of cervical cancer. The impact of the vaccine on the prevalence of HPV related carcinomas of the UADT is currently not known but likely beneficial.

Validity of sampling error as a cause of noncorrelation

BACKGROUND

Sampling error is a common explanation of noncorrelation in women whose Papanicolaou (Pap) tests show high-grade intraepithelial lesions (HSIL) but whose follow-up cervical biopsies show only cervical intraepithelial neoplasia (CIN) 1, koilocytosis, or reactive/inflammatory changes. The purpose of this study was to demonstrate the validity of sampling error in this setting by determining the proportion of negative colposcopic cervical biopsies in women with HSIL who subsequently undergo cone/loop electrode excision procedure (LEEP) biopsies or repeat cervical biopsies that confirm the diagnosis of high-grade CIN (HGCIN).

METHODS

In all, 368 cases of HSIL were retrieved from the computerized database from January 1, 2003 to December 31, 2005. Follow-up was obtained as part of routine quality assurance/quality control activities including cytologic-histologic correlation.

RESULTS

A total of 368 HSIL Pap diagnoses were retrieved. Of the 254 cases that were followed up by cervical biopsy, 146 showed HGCIN in the biopsy. Of the remaining 108 patients whose cervical biopsies failed to demonstrate HGCIN, 47 had a subsequent procedure, either cone/LEEP, cervical biopsy, or repeat Pap test. Cone biopsy/LEEP was performed in 34 cases (72.3%) with a diagnosis of HGCIN in 19. Repeat cervical biopsy was performed in 9 cases (19.1%) with HGCIN diagnosed in 5. Repeat Pap test was performed in 4 cases (8.5%) with HSIL diagnosed in 2.

CONCLUSIONS

In the population of women with HSIL by Pap test followed up by cervical biopsy with or without subsequent cone/LEEP, there was a discordant cervical biopsy rate for HGCIN of 43%. In the subgroup of women with HSIL by Pap test followed up by cervical biopsy and subsequent cone/LEEP or repeat cervical biopsy, the proportion of women with negative colposcopic cervical biopsy and subsequent histology-proven HGCIN was 56%. These figures justify sampling error as a valid cause of noncorrelation in women with HSIL followed up by cervical biopsy alone.

The negative predictive value of p16INK4a to assess the outcome of cervical intraepithelial neoplasia 1 in the uterine cervix

The immunohistochemical expression of p16 in formalin-fixed and paraffin-embedded histological sections was evaluated in a retrospective study comprising a low-grade group of 100 cases of cervical intraepithelial neoplasia (CIN) 1, a high-grade group of 50 cases of CIN 2 to 3, and a benign group of 50 cases of normal tissue or benign lesions in the uterine cervix. The cases were consecutive within each group and had a minimum follow-up period of 5 years. Positive reaction for p16 was detected in all cases in the high-grade group and in only 3 cases in the benign group. In the low-grade group, a total of 9 cases had to be excluded. The remaining 91 cases in the low-grade group showed positive reaction for p16 in 65 cases (71%), including 23 cases that progressed to a high-grade lesion, 36 cases that revealed normal cytological and/or histological picture during the follow-up period, and 6 cases that persisted as CIN 1. A total of 26 cases (29%) in the low-grade group showed negative reaction for p16. All but one of these p16 negative cases in the low-grade group had a benign or normal outcome. This case showed a high-grade lesion in the follow-up period and was probably a high-grade lesion from the beginning and so underestimated as CIN 1. These results reveal that the negative predictive value of p16 to predict the outcome of the cases of CIN 1 is as high as 96%, which strongly suggest an important role of p16 in the assessment of this type of lesion.

Profiling microdissected epithelium and stroma to model genomic signatures for cervical carcinogenesis accommodating for covariates

This study is the first comprehensive, integrated approach to examine grade-specific changes in gene expression along the entire neoplastic spectrum of cervical intraepithelial neoplasia (CIN) in the process of cervical carcinogenesis. This was accomplished by identifying gene expression signatures of disease progression using cDNA microarrays to analyze RNA from laser-captured microdissected epithelium and underlying stroma from normal cervix, graded CINs, cancer, and patient-matched normal cervical tissues. A separate set of samples were subsequently validated using a linear mixed model that is ideal to control for interpatient gene expression profile variation, such as age and race. These validated genes were ultimately used to propose a genomically based model of the early events in cervical neoplastic transformation. In this model, the CIN 1 transition coincides with a proproliferative/immunosuppression gene signature in the epithelium that probably represents the epithelial response to human papillomavirus infection. The CIN 2 transition coincides with a proangiogenic signature, suggesting a cooperative signaling interaction between stroma and tumor cells. Finally, the CIN 3 and squamous cell carcinoma antigen transition coincide with a proinvasive gene signature that may be a response to epithelial tumor cell overcrowding. This work strongly suggests that premalignant cells experience a series of microenvironmental stresses at the epithelium/stroma cell interface that must be overcome to progress into a transformed phenotype and identifies the order of these events in vivo and their association with specific CIN transitions.

Evaluation of p16INK4a, minichromosome maintenance protein 2, DNA topoisomerase IIα, ProEX C, and p16INK4a/ProEX C in cervical squamous intraepithelial lesions

p16INK4a has been shown to be overexpressed in nearly all high-grade squamous intraepithelial lesions (HSILs). Other cell-cycle regulators, such as minichromosome maintenance protein 2 (MCM2), DNA topoisomerase IIalpha (TOP IIA), and ProE(X) C (a cocktail of MCM2 and TOP IIA), have also demonstrated some value in identifying squamous intraepithelial lesions. Data on direct comparison of those cell regulatory proteins in the detection of squamous intraepithelial lesions, with a focus on low-grade squamous intraepithelial lesions (LSILs), are limited. We immunohistochemically evaluated the diagnostic value of p16, MCM2, TOP IIA, ProE(X) C, and a cocktail of p16 and ProE(X) C in 62 cervical biopsy specimens, including 14 cases of benign squamous mucosa (group 1), 34 cases of LSILs (group 2), and 14 cases of HSILs (group 3). The staining intensity and distribution were recorded. The results demonstrated that positive staining for p16 and the p16/ProE(X) C was observed in 100% of cases in group 3, whereas 79%, 86%, and 79% of cases were positive for CM2, TOP IIA, and ProE(X) C, respectively. ProE(X) C and the p16/ProE(X) C showed positive staining in 94% and 100% of cases in group 2, respectively. In contrast, immunoreactivity for p16, MCM2, and TOP IIA was detected in only 76% of cases in group 2. Importantly, all 8 p16-negative cases in group 2 were positive for p16/ProE(X) C (P = .003). Our data indicate that (1) p16 is a more sensitive and specific marker for identifying HSILs; (2) ProE(X) C is a better marker for the detection of LSILs; and (3) p16/ProE(X) C provides the highest diagnostic value for the detection of both HSILs and LSILs.

Human papillomavirus DNA integration and messenger RNA transcription in cervical low- and high-risk squamous intraepithelial lesions in Austrian women

The human papillomavirus (HPV) plays an important role in the progression of cervical carcinoma. High-risk (HR) HPV types have been mainly identified in cytologic high-grade squamous intraepithelial lesions (HSILs) and histologic invasive carcinoma of the cervix. We examined cervical swabs of patients with abnormal Papanicolaou (Pap) smears, diagnosed as low-grade squamous intraepithelial lesions (LSILs) including atypical squamous cells of uncertain significance or HSILs. Low-risk (LR) HPV and HR-HPV types were identified by the Digene Hybrid Capture II test. Two-dimensional (2D) gel electrophoresis was used to specify the physical state of HPV DNA sequences. Expression of E6/E7 messenger RNA (mRNA) transcripts was analyzed by reverse transcriptase-polymerase chain reaction. Histopathologic results were correlated to the patients' physical status and HPV DNA mRNA transcripts. Pap smears with HPV infections of LR and HR types were correlated to the degree of squamous intraepithelial lesions (SILs). Comparing the physical states of HPV DNA sequences with the expression of HPV E6/E7 mRNA transcripts, all types were identified only as extrachromosomal in benign cervical smears, cervical intraepithelial neoplasia (CIN) I and II. HPV16 showed all physical states in CIN III/carcinoma in situ (CIS), whereas HPV18 only existed in mixed and integrated forms. HPV31/33/52b/58 appeared in all stages of lesions most commonly in extrachromosomal form; in integrated form, they were present only in CIN III/CIS. Although integration of some HR-HPV types is not always necessary for progression of SILs, the above-mentioned method is useful to analyze the physical state of HPV DNA sequences and predict the progression of SILs.

High-grade ovarian serous carcinoma exhibits significantly higher p16 expression than low-grade serous carcinoma and serous borderline tumour

AIMS

A dualistic pathway of ovarian serous carcinogenesis is now well established whereby high-grade serous carcinoma and low-grade serous carcinoma represent two distinct tumour types with a different underlying pathogenesis. The aim of this study was to compare expression of p16 INK4A (p16) in these two tumour types. We also included cases of serous borderline tumour, since these are considered to represent a precursor lesion of low-grade serous carcinoma.

METHODS AND RESULTS

Cases of serous borderline tumour (n = 18), low-grade ovarian serous carcinoma (n = 22) and high-grade ovarian serous carcinoma (n = 24) were stained with a monoclonal antibody against p16. Cases were scored both with respect to intensity of immunoreactivity (weak, 1+; moderate, 2+; or strong, 3+) and distribution (0, negative or occasional positive cells; 1+, < 10% cells positive; 2+, 10-25% cells positive; 3+, 26-50% cells positive; 4+, 51-75% cells positive; or 5+, 76-100% cells positive). An immunohistochemical composite score was also calculated (0-15) by multiplying the intensity and distribution scores. There was a statistically significant difference in p16 immunoreactivity with respect to intensity, distribution and composite score between high-grade serous carcinoma and each of the other two groups, with the high-grade neoplasms exhibiting stronger and more diffuse positivity. Most high-grade serous carcinomas exhibited positivity of close to 100% of tumour cells. There was no significant difference in p16 expression between the borderline tumours and low-grade serous carcinomas.

CONCLUSIONS

The increased expression of p16 in high-grade serous carcinoma compared with low-grade serous carcinoma and serous borderline tumour is in keeping with a different underlying pathogenesis. p16 may be implicated in the development of high-grade serous neoplasia within the ovary and elsewhere within the female genital tract.

Efficiency of immunohistochemical p16 expression and HPV typing in cervical squamous intraepithelial lesion grading and review of the p16 literature

Diagnosing and grading cervical cancer precursors is challenging. This study investigates the presence of HPV infection, the expression of p16, and any correlation between these two findings. H&E-stained slides of cervical loop excision materials diagnosed as LSIL and HSIL were reviewed. An immunohistochemical panel consisting of p16 as well as of all HPV types and HR-HPV types was applied. Staining of p16 was evaluated according to distribution extent and degree of intensity. All HSIL cases and 80% of LSIL cases were positive for p16. In HSIL cases, the staining distribution was as follows: 50% full thickness, 45% basal, and 5% rare. The staining intensity for the same cases was strong in 70%, variable in 20%, and weak in 10% accordingly. In LSIL cases, staining distribution was basal in 58.3% and rare in 41.7%. None of the LSIL cases showed full thickness of p16 positivity. The staining intensity of the same cases was strong in 25%, variable in 16.7%, and weak in 58.3%. Of all cases, 48.6% were positive for screening kit (all HPV types), and 31.4% of all cases were positive for HR-HPV. The distribution of this positivity was 35% for HSIL and 26.6% for LSIL cases. The total HPV-type positivity rate was 48.6%, the distribution being 50% for HSIL and 46.6% for LSIL cases. p16 is a highly sensitive marker for cervical epithelial dysplasia. Strong and full thickness staining of p16 in the cervix epithelium is highly supportive of HSIL, while weak and basal/rare staining favors LSIL. All HPV-positive cases were also p16-positive, but no statistically significant relationship between HPV infection positivity and the intensity and distribution of p16 was found. HPV is not helpful in the grading of SIL, as an unignorable rate of HR-HPV positivity (26.6%) was detected in LSIL group.

P16INK4a expression, human papillomavirus, and survival in head and neck cancer

Development of head and neck cancer (HNC) is associated with human papillomavirus high-risk (HPV-HR) types. The HPV E7 oncoprotein inactivates the pRB protein increasing expression of p16(INK4a). P16 expression and HPV status have been associated with differences in clinical outcomes for HNC. This study examined whether HNC prognosis was different when these biomarkers were examined as individual or joint molecular effects. Tumor tissue from 301 HNC patients were analyzed and sequenced for HPV types. P16 was evaluated by immunohistochemical staining. p16 was expressed in 35% and HPV-HR was detected in 27% of HNC patients. After adjustment for age, tobacco, and alcohol, p16+ tumors were statistically significantly associated with HPV-HR (OR=13.3, 7.1-24.9), histology, stage, grade, tumor site, and node involvement. Compared to p16+ HNC cases, those who did not express p16 had significantly worse disease-specific (DS) survival (Hazards Ratio, adj.HR=2.0. 1.0-3.9) and recurrence (adj.HR=3.6, 1.6-8.2); and HPV- cases had worse DS survival (adj.HR=2.8, 1.1-7.1) and recurrence (adj.HR=2.0, 0.8-4.8) compared to HPV-HR patients. Each of the p16/HPV groups had different survival outcomes: p16+/HPV-HR cases (referent) had the best and p16-/HPV- cases had the worst DS survival (adj.HR=3.6; 53% versus 13%, p=0.004) whereas p16+/HPV- and p16-/HPV-HR had similar DS survival (adj.HR=2.7/2.8). p16-/HPV-HR cases had a worse recurrence rate (adj.HR=7.0; 60% versus 0%, referent, p=0.08) than p16-/HPV- (adj.HR=4.5) or p16+/HPV- (adj.HR=1.8) cases. The combined p16/HPV biomarker data are associated with different survival outcomes of HNC compared to each marker evaluated separately, indicating that the two molecular mechanisms evaluated together may provide a more accurate prediction of clinical outcomes.

Clinicopathological Roles of Alterations of Tumor Suppressor Gene p16 in Papillary Thyroid Carcinoma

BACKGROUND

Alterations of the p16 gene are common in human cancers, but their roles in thyroid cancers have not been clearly defined. The aim of the present study was to investigate the clinicopathological roles of the p16 gene in papillary thyroid carcinoma (PTC).

METHODS

p16 gene alterations were investigated in 44 patients with PTC (9 men, 35 women) by immunohistochemistry, reverse transcriptase-polymerase chain reaction and methylation-specific polymerase chain reaction. The findings were correlated with their clinicopathological features.

RESULTS

p16 protein expression, mRNA alterations, and promoter methylation were detected in 89% (n = 39), 77% (n = 33), and 41% (n = 18) of patients with PTC, respectively. There was no marked relationship between p16 protein expression, mRNA alteration, and promoter methylation. In follicular variant of PTC (FVPTC), there was a frequent lack of p16 protein expression and promoter methylation. PTCs showing p16 promoter methylation were often associated with a high AMES (age, metastasis to distant sites, extrathyroidal invasion, size) risk group and advanced pTNM (tumor-lymph node-metastasis) stages.

CONCLUSIONS

p16 gene alterations are common and correlate with histological features and biological aggressiveness in PTC, suggesting that they might play an important role in its pathogenesis.

Immunohistochemical detection of p16INK4a in dysplastic lesions of the oral cavity

Significant intra- and interobserver variability exists in diagnosing and grading oral epithelial dysplasia. Mutations in the tumor-suppressor gene p16 are common in oral cavity dysplastic lesions, but whether immunohistochemical detection of the gene product p16(INK4a) (p16) can be used as a reliable biomarker for dysplasia is unclear. In total, 119 biopsy specimens representing various oral cavity sites and degrees of dysplasia were retrieved from the pathology files of Emory University Hospital. Formalin-fixed, paraffin-embedded sections were stained with hematoxylin and eosin (H&E) and with a monoclonal antibody to p16 (LabVision Corporation, Clone JC2). A blinded review of the H&E slides and the pattern and degree of p16 expression was independently performed by two pathologists. A consensus was obtained when diagnoses differed. Morphologic diagnoses were then compared to p16 immunohistochemical expression. Overall, 61/119 (51%) cases showed no p16 immunoreactivity, including 12/33 (36%) cases of no dysplasia, 11/28 (39%) cases of mild dysplasia, and 38/58 (66%) cases of moderate/severe dysplasia. The remaining cases showed p16 expression limited to the basal and suprabasal nuclei and generally confined to the lower one-third of the epithelium. A logistic regression model showed a trend toward absent p16 expression with increasing severity of dysplasia (P=0.006). Decreased expression of p16 in dysplastic lesions, as found in this study, may reflect the biologic events involving loss of p16 gene function in the pathogenesis of oral cancer. Our findings suggest that p16 immunohistochemistry is not helpful in differentiating dysplastic from nondysplastic mucosa in oral cavity biopsies, and thus is not a reliable biomarker for use in routine clinical practice.

Expression of p16(INK4a) in relation to histopathology and viral load of 'high-risk' HPV types in cervical neoplastic lesions

A total of 91 cervical archival biopsy series were analysed for the presence and viral load of 'high-risk' types of human papillomavirus (HR-HPV), and p16(INK4a) expression. The women had various degrees of CIN (cervical intraepithelial neoplasia). HPV 16 was the most prevalent type found, at 47% frequency. The frequency of HPV 16 increased with increasing immunoreactivity to p16(INK4a), from 39% to 44% at cases scored low to medium, to 65% at high reactivity. Thirty (33%) of the samples had negative p16(INK4a) analysis results, but were positive for HR-HPV. There was no significant correlation between viral load and the level of p16(INK4a) expression, while the grade of CIN correlated to such expressions. Thus, p16(INK4a) expression analysis yielded information which is consistent with results from the histopathology and might complement the HPV analysis in a clinical prognostic procedure in order to find women at risk for cervical cancer.

Chapter 10: New dimensions in cervical cancer screening

Human papillomavirus (HPV) testing has clearly demonstrated a higher sensitivity but somewhat lower specificity than cytology. However, there are still issues regarding how best to use it in primary screening. In countries where cytology is of good quality, the most interesting possibility for primary screening is to use HPV testing as the sole screening modality with cytology reserved for triage of HPV-positive women. In countries with a less established infrastructure, however, use of HPV alone would also be attractive, although rapid, simple tests followed by immediate treatment are needed to minimize the number of visits and make best use of limited resources. Several approaches to deal with the lower specificity of HPV testing are also examined. These include HPV typing with a different management strategy for HPV-16 and -18/45, use of viral load to exclude infections unlikely to be associated with > or =CIN-2, and markers of proliferative lesions such as p16 and mRNA or cell-cycle markers such as cdc6 or the mcm5 proteins. Micro-array studies offer the prospect of discovering new, better DNA- or RNA-based diagnostics. The fact that HPV is a sexually transmitted infection may lead to anxiety and concerns about sexual relationships and these issues are also discussed. Ongoing HPV studies are identified and briefly reviewed.

Molecular biology of human papillomavirus infection and cervical cancer

HPVs (human papillomaviruses) infect epithelial cells and cause a variety of lesions ranging from common warts/verrucas to cervical neoplasia and cancer. Over 100 different HPV types have been identified so far, with a subset of these being classified as high risk. High-risk HPV DNA is found in almost all cervical cancers (>99.7%), with HPV16 being the most prevalent type in both low-grade disease and cervical neoplasia. Productive infection by high-risk HPV types is manifest as cervical flat warts or condyloma that shed infectious virions from their surface. Viral genomes are maintained as episomes in the basal layer, with viral gene expression being tightly controlled as the infected cells move towards the epithelial surface. The pattern of viral gene expression in low-grade cervical lesions resembles that seen in productive warts caused by other HPV types. High-grade neoplasia represents an abortive infection in which viral gene expression becomes deregulated, and the normal life cycle of the virus cannot be completed. Most cervical cancers arise within the cervical transformation zone at the squamous/columnar junction, and it has been suggested that this is a site where productive infection may be inefficiently supported. The high-risk E6 and E7 proteins drive cell proliferation through their association with PDZ domain proteins and Rb (retinoblastoma), and contribute to neoplastic progression, whereas E6-mediated p53 degradation prevents the normal repair of chance mutations in the cellular genome. Cancers usually arise in individuals who fail to resolve their infection and who retain oncogene expression for years or decades. In most individuals, immune regression eventually leads to clearance of the virus, or to its maintenance in a latent or asymptomatic state in the basal cells.

p16 expression in the female genital tract and its value in diagnosis

p16 is a cyclin-dependent kinase-4 inhibitor that is expressed in a limited range of normal tissues and tumors. In recent years, immunohistochemistry with p16 antibodies has been used as a diagnostic aid in various scenarios in gynecologic pathology. Diffuse (as opposed to focal) positivity with p16 in the cervix can be regarded as a surrogate marker of the presence of high-risk human papillomavirus (HPV). In cervical squamous lesions, p16 is positive in most high-grade cervical intraepithelial neoplasia (CIN) and in some cases of low-grade CIN, usually those associated with high-risk HPV. p16 may be useful to identify small focal high-grade CIN lesions, to distinguish some cases of CIN involving immature metaplastic squamous epithelium from immature metaplastic squamous epithelium not involved by CIN and to distinguish high-grade CIN from benign mimics. Most cervical carcinomas of squamous, glandular, and small cell type are p16-positive. In cervical glandular lesions, p16 is useful, as part of a panel, in the distinction between adenocarcinoma in situ (diffusely positive) and benign mimics, including tuboendometrial metaplasia and endometriosis, which are usually p16-negative or focally positive. p16 may be used, in combination with other markers, to distinguish between a cervical adenocarcinoma (diffuse positivity) and an endometrioid-type endometrial adenocarcinoma (negative or focally positive). Some uterine serous carcinomas are diffusely positive. In the vulva, p16 is positive in HPV-associated vulval intraepithelial neoplasia (VIN) but negative in VIN not associated with HPV. Similarly, HPV-associated invasive squamous carcinomas are p16-positive, whereas the more common non-HPV-associated neoplasms are largely negative or focally positive. In the uterus, p16 positivity is more common and widespread in leiomyosarcomas than leiomyomas, and this may be a useful aid to diagnosis, although problematic uterine smooth muscle neoplasms have not been extensively studied. Metastatic cervical adenocarcinomas in the ovary are usually diffusely p16-positive, and because these may closely mimic a primary ovarian endometrioid or mucinous adenocarcinoma, this may be a valuable diagnostic aid, although p16 expression in primary ovarian adenocarcinomas of these morphologic subtypes has not been widely investigated. Some ovarian serous carcinomas, similar to their uterine counterparts, are p16-positive.

Impact of utilizing p16INK4A immunohistochemistry on estimated performance of three cervical cancer screening tests

The histopathological diagnosis of cervical intraepithelial neoplasia grade 2,3 (CIN 2,3) is subjective and prone to variability. In our study, we analyzed the impact of utilizing a biomarker (p16(INK4A)) together with histopathology to refine the "gold standard" utilized for evaluating the performance of 3 different cervical cancer screening tests: cervical cytology, human papillomavirus (HPV) DNA testing and visual inspection with acetic acid (VIA). Cervical biopsies from 2 South African cervical cancer screening studies originally diagnosed by a single pathologist were reevaluated by a second pathologist and a consensus pathology diagnosis obtained. Immunohistochemical staining for p16(INK4A) was then performed. The estimated sensitivity of some cervical cancer screening tests was markedly impacted by the criteria utilized to define CIN 2,3. Use of routine histopathology markedly underestimated the sensitivity of both conventional cytology and HPV DNA testing compared to an improved gold standard of consensus pathology and p16(INK4A) positivity. In contrast, routine histopathology overestimated the sensitivity of VIA. Our results demonstrate that refining the diagnosis of CIN 2,3 through the use of consensus pathology and immunohistochemical staining for p16(INK4A) has an important impact on measurement of the performance of cervical cancer screening tests. The sensitivity of screening tests such as HPV DNA testing and conventional cytology may be underestimated when an imperfect gold standard (routine histopathology) is used. In contrast, the sensitivity of other tests, such as VIA, may be overestimated with an imperfect gold standard.