p16 Positive Histologically Bland Squamous Metaplasia of the Cervix: What does It Signify?

Copy Number Profiling Implicates Thin High-Grade Squamous Intraepithelial Lesions as a True Precursor of Cervical Human Papillomavirus-Induced Squamous Cell Cancer

Full-thickness high-grade squamous intraepithelial lesions (HSIL) are precursors of invasive cervical squamous cell carcinoma (SCC). The World Health Organization and Lower Anogenital Squamous Terminology Standardization Project for human papilloma virus (HPV)-associated lesions divide full-thickness HSIL of the cervix into thin HSIL with thickness of 1 to 9 cell layers and the typical full-thickness HSIL of >10 cell layers. Although HPV oncogene transcripts and p16ink4a overexpression, as markers of transforming HPV infection, are detectable in thin HSIL, the biological significance of thin HSIL in cervical carcinogenesis remains poorly understood. To further characterize thin HSIL, we performed a comparative study of chromosomal copy number variations (CNV), an analysis of dysregulated genes present in the segments with CNV, and a generalized genetic complexity calculation for 31 thin HSIL, 31 thick HSIL, 24 microinvasive SCC (pT1a SCC), and 22 highly invasive SCC samples. Thin HSIL share various CNV and specific dysregulated gene pathways with thick HSIL and invasive SCC. Thin HSIL exhibited an average CNV of 11.6% compared with 14.1% for thick HSIL, 15.5% for pT1a SCC, and 26.6% for highly invasive SCC. The CNV included gains at 1q and 3q (40% and 43%, respectively), partial loss of 3p, and loss of chromosomes 11 (18%), 16 (50%), 20 (35%), and 22 (40%). Pathways affected solely in thin HSIL were those enhancing immune evasion and primarily involved the (interleukin) IL6, IL21, and IL23 genes. ILs are transiently upregulated in response to infection and play a crucial role in mounting antitumor T-cell activity. Deregulation reflects an attempt by the HPV to evade the initial immune response of the host. The primary pathways shared by thick HSIL and invasive SCC were interactions between lymphoid and nonlymphoid cells, NOTCH2 signaling, tight junction interactions (primarily of the claudin family), and FGR2 alternative splicing. Our results show that thin HSIL carry similar genetic changes as thick HSIL and SCC, indicating that thin HSIL are true precursor lesions that can progress to thick HSIL and SCC.

Acquisition of Genetic Aberrations During the Progression of High-Grade Intraepithelial Lesions/Micro-Invasive Squamous Cancers to Widely Invasive Cervical Squamous Cell Cancer

CONTEXT.—

Acquisition of genetic aberrations during cervical carcinogenesis in individual patients is poorly documented.

OBJECTIVE.—

To provide a comparative analysis of high-grade squamous intraepithelial lesions (n = 7) and pT1a squamous cancers (n = 1) and their recurrences, subsequent widely invasive cancers, and metastases developed during 1-24 years.

DESIGN.—

Archival tissues of 8 patients were analyzed immunohistochemically for reserve-cell origin, human papillomavirus genotypes, mutations in 50 cancer genes, and chromosomal copy number variations.

RESULTS.—

Intraepithelial lesions arose either from cytokeratin 17- or 7-expressing reserve cells. All preinvasive and invasive tumors carried human papillomavirus high-risk genotypes and lacked somatic mutations. Chromosomal copy number variations were identified in all intraepithelial lesions and invasive cancers. Four of 8 high-grade intraepithelial lesions progressed to invasive cancer after incomplete treatment, and 4 of 8 invasive cancers arose de novo after in sano resection. Four of 8 cancers carried mutations with high mutational frequency (PIK3CA E545K [n = 2]; PIK3CA and SMAD1 [n = 1]; HRAS, RB1, and EGFR [n = 1]), as did their corresponding regional metastases. One nonmetastasized cancer had a subclonal PIK3CA mutation, and an initially nonmutated, low-stage cancer developed ovarian metastases with PIK3CA amplification. One patient had neither mutations nor metastases. The patient with treated PIK3CA E545K-mutated pT1a cancer developed a subsequent nonmutated intraepithelial lesion that progressed to invasive cancer with a subclonal PIK3CA-H1047R mutation. Cancer-related deaths in 4 of 8 (50%) patients occurred independent of mutational status or metastatic disease.

CONCLUSIONS.—

Recurrences arose after persistent or de novo human papillomavirus infection of residual reserve cells or squamous metaplasia. Activating driver mutations were identified in invasive cancers only. High mutational load correlated with metastases, which in turn represented clonal disease.

Cervical Precancers Originate From Infected Proliferating Reserve Cells: A Comparative Histologic and Genetic Study of Thin and Thick High-grade Squamous Intraepithelial Lesions

Human papillomavirus (HPV)-induced invasive cervical squamous cell cancer (SCC) develop via high-grade squamous intraepithelial lesion (HSIL). In contrast to classic thick HSIL, thin HSIL (≤9 cell layers) are poorly documented. This study compares histology, HPV genotypes, and aberrations in 50 cancer genes of 45 thin HSIL to 45 thick HSIL, 20 pT1a SCC, and 40 ≥pT1b SCC. Thin HSIL arose from proliferating reserve cells within endocervical epithelium or immature metaplasia throughout the transformation zone after infection with high-risk HPV genotypes (36/45; 80%), and 20% non-high-risk HPV genotypes compared with 2.5% thick HSIL, pT1a SCC, and ≥pT1b SCC. Thin HSIL were multifocal proliferations with varying epithelial thickness between 1 and 2 to 9 cell layers, with occasional transitions to thick HSIL or concomitant lesions of thick HSIL. Overall, 40% thin HSIL were located distant to and most thick HSIL occurred near or at the squamocolumnar junction. Only 20% thick HSIL showed koilocytosis. All HSIL lacked somatic gene mutations, compared with 30% pT1a and 55%≥pT1b SCC. Overrepresented rare germline variants in the MET, JAK3, and FGFR3 genes occurred in all patient groups. In summary, thin and thick HSIL arose independently of somatic gene mutations. The maturation level of the squamous epithelium at the time of transforming infection determines if a thick HSIL develops directly from HPV-infected proliferating reserve cells via thin HSIL or in stratified glycogenated squamous epithelium via low-grade squamous intraepithelial lesion. These observations raise doubts about the biological relevance of separation into thin and thick HSIL. The oncogenic potential of HPV genotypes but also germline variants may influence the natural history.

The origin of Human Papillomavirus (HPV) - induced cervical squamous cancer

Most research models of HPV-associated squamous cervical carcinogenesis focus on stratified glycogenated squamous epithelium, a permissive environment for HPV-life-cycle completion, while immature squamous metaplastic epithelium and reserve cells as targets of HPV-infection have received less attention. Subcolumnar reserve cells of urogenital sinus origin with a CK17/p63-phenotype serve as the primary stem cell for squamous metaplasia. The area of manifest or potential squamous metaplasia, referred to as transformation zone, is the site where most squamous cancers occur after a transforming HPV infection of proliferating reserve cells and/or metaplastic epithelium. Improper use of terminology, in particular confusion of transformation zone with transition zone (synonymous: squamous-columnar junction or SCJ), as well as poorly substantiated postulates of a stem cell niche at the squamous-columnar junction with 'embryonic stem cell markers' have complicated understanding of HPV-related squamous carcinogenesis. Reserve cells as target cells and reservoirs of HPV should move into future research focus.

Evaluating the Performance of p16INK4a Immunocytochemistry in Cervical Cancer Screening

Purpose

When used for cervical cancer primary screening, liquid-based cytology (LBC) has a high specificity but a low sensitivity. For histological diagnosis of high-grade lesions, p16^INK4a immunostaining has proven to be useful. Therefore, our objective was to evaluate the use of p16^INK4a immuno-cytology as a primary screen and a secondary screen after primary high-risk human papillomavirus (hrHPV) screening or LBC screening.

Methods

A total of 1197 cytology slides were immuno-stained using automatic p16^INK4a staining system (PathCIN^®p16^INK4a) in two studies from cervical screening programs. In the primary screening study, 875 slides were randomly selected and analyzed for p16^INK4a. In the secondary screening study, 322 of the remaining slides were chosen by virtue of being HPV 16/18+, other hrHPV+/LBC≥ASC-US, or HPV-negative/LBC ≥LSIL. The sensitivity and specificity for detection of cervical intraepithelial neoplasia 2/3 or worse (CIN2+/CIN3+) were compared based on p16^INK4a, LBC and HPV test results.

Results

In combining two studies, there were 431 cases with biopsy pathology. They included 83 cases with CIN2+ and 41 cases with CIN3+. The p16 positivity rate increased with pathologic and cytologic severity (P<0.0001). For primary screening: p16 immuno-cytology was more specific than HPV testing and was similar in sensitivity. Also, p16 immuno-cytology compared favorably with routine LBC (≥ASC-US or ≥LSIL) in sensitivity and specificity. For secondary screening: after LBC screening, “Triaging ASC-US with p16” gave a higher specificity and a similar sensitivity as compared to the “Triaging ASC-US with hrHPV” algorithm. After HPV primary screening, p16 immuno-cytology was more specific than LBC (≥ASC-US); the calculated colposcopy referral rate was also decreased by using p16 immuno-cytology as triage. Triage of “HPV16/18 and p16” had higher specificity and similar sensitivity as compared to triage of “HPV16/18 and LBC ≥ASC-US”.

Conclusion

For primary screening, p16^INK4a immuno-cytology compares favorably to routine LBC and HPV testing. p16^INK4a immunostaining could be an efficient triage to reduce the colposcopy referral rate after primary hrHPV screening or LBC screening. Therefore, p16^INK4a immuno-cytology may be applicable as a favorable technology for cervical cancer screening.