High-Grade Squamous Intraepithelial Lesion of the Cervix

Etiology

Scientific studies have established HPV as the primary etiologic agent in the pathogenesis of cervical dysplasia and carcinoma. HPV is a non-enveloped double-stranded DNA virus within the Papillomaviridae family. There are over 150 genotypes of HPV, with 40 known to infect the anogenital tract. These 40 genotypes are divided into high-risk and low-risk groups based on evidence of their oncogenic potential. HPV 16 and HPV 18 are high-risk genotypes found in over 70% of HSILs and cervical squamous cell carcinomas. Contrary to low-grade squamous intraepithelial lesions (LSIL), which represent transient HPV infections that are cleared within 2 to 5 years and have a low risk of malignancy, HSILs are associated with persistent infection and a greater risk of progression to invasive cervical cancer, especially if the persistent infection is a high-risk genotype such as HPV 16 and/or HPV 18.[2]

Epidemiology

Since HSIL is caused by HPV infection, it is found more commonly in women with specific genetic and behavioral factors which increase their risk of acquiring HPV. HPV prevalence is highest in young, sexually active females, then progressively drops until menopause, with some studies showing a slight increase after menopause. This decline in middle age is thought to result from an effective immune response after exposure to HPV and the likelihood of less exposure to HPV. An immunocompromised state, such as after transplant therapy and in HIV-infected individuals, increases a patient’s risk of persistent HPV infection and the development of a squamous intraepithelial lesion (SIL).

Studies indicate a younger age at sexual debut and a higher number of sexual partners increase the risk of HPV infection as well as more recent sexual activity. Male partner promiscuity is also a factor. Condom use and circumcision can reduce the risk of HPV infection.[3] Studies have demonstrated no difference in the prevalence of HPV infection based on sexual orientation.[4] Multiparous women, with specifically >7 births, are also at increased risk.

There is a strong association between smoking and cervical neoplasia, independent of HPV status, presumably due to the presence of carcinogens within the cervical mucus. Certain HLA class II alleles and haplotypes, notably HLA DRB1*07 and HLA-DQB1*03, have a positive association with SILs and invasive cancer, with evidence suggesting that the haplotypes may influence HPV antigen presentation and immune response.[5][6]  Other HLA class II haplotypes have been found to be protective. Oral contraceptive use may somewhat increase a patient’s risk of cervical neoplasia, but there is a minimal negative impact on the absolute risk.[7][8][9][10]

Pathophysiology

The genome of HPVs includes the early genes (E1, E2, E4, E5, E6, E7), involved in the regulation of the vegetative and proliferative phases of the viral life cycle, the late genes (L1, L2), which encode the capsid proteins, and a non-coding long control region (LCR) involved in viral replication and transcription regulation. HPV infects the basal epithelial cells of the transformation zone after gaining entry through microabrasions. A class of cell surface receptors on the keratinocytes called heparan sulfate proteoglycans (HSPG) are thought to be the initial receptors for the virus, attaching to L1 of the capsid and inducing conformational changes and subsequent cleavage of L2. The viral genome is slowly internalized over a 12-hour period through clathrin or caveolae-mediated endocytosis. Entry of the viral genome into the nucleus occurs through nuclear membrane breaks. Viral replication then begins. As the basal cells mature and reach the terminally differentiated layer of epithelium, expression of the L1 and L2 capsid proteins occurs to enable the assembly of viral particles, which are sloughed off along with the dead squamous cells, allowing continued transmission and infection of the virus. This is the typical life cycle of most HPV genotypes.[2][11]

High-risk HPV types, especially HPV 16, have often been shown to integrate their genome into the human genome. Integration has been proposed as an early event in the progression of LSIL to HSIL. It involves the viral oncoproteins E6 and E7 maintaining double-strand breakpoints in host DNA by attenuating the DNA-damage response (DDR) involved in repairing such breaks so that the viral genome can integrate at these breakpoints. The high-risk HPV E6 oncoprotein is known to interfere with p53, a cellular tumor-suppressor protein required for sensing base excision repair machinery and repairing oxidative damage, by inducing increased proteasome-dependent degradation of p53. High-risk HPV E7 oncoprotein inactivates members of the retinoblastoma (Rb) tumor suppressor protein family.

Retinoblastoma is coupled with an E2F transcription factor. Inactivation of Rb uncouples E2F, thus allowing it to upregulate genes required for S-phase entry and progression. The aforementioned E6 and E7 interactions are just glimpses of how these oncoproteins interact with various proteins in the nucleus. Essentially, overexpression of E6/E7 causes cell cycle dysregulation. Studies suggest integration also causes host gene expression changes, amplifying oncogenes and disrupting tumor suppressor genes. As the HPV genome is double-stranded and integrated into the host genome, it effectively evades the immune response leading to persistent infection. Epigenetic modification of various genes and changes in the expression of microRNAs have also been shown to play a role in carcinogenesis. Much remains to be elucidated regarding the molecular pathogenesis of cervical neoplasia.[2][11]

Histopathology

Diagnosis of HSIL on cytology requires specific criteria to be met. The cells are smaller, with less cytoplasmic maturity than that of LSIL. Occasionally, the cytoplasm may be densely keratinized. HSIL cells occur singly as well as in sheets or syncytial aggregates. Though the size of the nucleus itself is variable, the cells must have a high nuclear-to-cytoplasmic ratio (see Image 1. HSIL of the Cervix, Nuclear-to-Cytoplasmic Ratio). The nuclei are often hyperchromatic but can range from normal to hyperchromatic. The chromatin can range from evenly distributed and fine to coarsely granular. Nuclear contours must be distinctly irregular with prominent indentations and/or grooves. Nucleoli are usually not a feature of HSIL, though may be seen when HSIL involves the endocervical glands.

Histologic criteria for HSIL exceeds the extent and degree of nuclear atypia allowed for a diagnosis of LSIL and includes less maturation, a higher nuclear-to-cytoplasmic ratio, decreased organization from the lower immature cell layers to the superficial mature layers (loss of polarity), a greater degree of nuclear pleomorphism, highly irregular nuclear contours, increased mitotic index, and abnormal mitotic figures, especially within more superficial layers of the epithelium (see Image 2. HSIL of the Cervix, Nuclear Membrane). CIN 3 must have full-thickness atypia. When faced with challenging biopsy specimens where the pathologist is debating between benign mimics of HSIL, such as immature metaplasia or atypical atrophy, utilizing the biomarker p16 may help distinguish them, as p16 shows intense and continuous staining in HSILs and suggests infection with a high-risk HPV type.[12][13][14]

History and Physical

Women with biopsy-proven HSIL will likely have a history of multiple risk factors for HPV infection, a positive HPV test, and/or a history of abnormal Pap tests. Abnormal colposcopic findings characteristic of high-grade changes include dense acetowhite epithelium, rapid appearance of acetowhitening, cuffed crypt openings, coarse mosaicism, coarse punctuation, a sharp border, an inner border sign, and a ridge sign. The inner border sign is a sharply demarcated acetowhite area within a less opaque acetowhite area. The ridge sign is the presence of thick ledges of opaque acetowhite epithelium growing irregularly within the squamocolumnar junction.[15][16][17]

Evaluation

A Papanicolaou (Pap) test is the preferred initial method of screening for cervical neoplasia. This test is performed by opening the vaginal canal with a speculum, fully visualizing the cervix, using a cervical broom or spatula to sample cells from the transformation zone, and transferring the cells either into liquid preservative (liquid-based cytology) or directly onto a microscope slide (conventional cytology). Pathology will process the specimens according to the type of test received.

The current American College of Obstetricians and Gynecologists (ACOG) recommendations for cervical carcinoma screening in women is dependent upon age, HIV infection/immunodeficiency, and pregnancy status. Screening should be initiated at 21 years of age. Women ages 21 to 29 should be screened by cytology every 3 years. Women ages 30 to 65 should be screened with cytology and HPV co-testing every 5 years or by cytology alone every 3 years. Depending on the HPV test used, the test will provide pooled results for high-risk HPV subtypes and/or individual genotype results for HPV 16 and 18. The risk of HSIL in a patient with a positive HPV test and an abnormal Pap test is approximately 20% and increases to 33% if HPV positive at more than 1 visit.[18]

The American Society for Colposcopy and Cervical Pathology (ASCCP) publishes comprehensive guidelines for managing patients based on their Pap-test and HPV-test results and risk. For women ages 21 to 24, colposcopy is recommended following an HSIL cytology diagnosis. Women older than 24 years should also have a colposcopy performed, though management with an excisional procedure is acceptable. About 60% of women with HSIL cytology will have at least CIN 2 on biopsy, with approximately 2% showing invasive cancer, though the latter is more likely in older women. Women older than 30 years have an 8% 5-year risk of cervical cancer after a diagnosis of HSIL. Biopsies taken during colposcopy are examined for histology.[19]

After spontaneous resolution or pertinent management of CIN 2, CIN 3, or adenocarcinoma in situ, routine screening should not be discontinued for at least 20 years (even if this extends beyond age 65).[20]

Treatment / Management

Women aged 21 to 24 with HSIL cytology are recommended to undergo colposcopy. If CIN 2 or greater is not diagnosed on biopsy, it is recommended the patient follow up with cytology and colposcopy every 6 months for a 24-month period, as long as exams are adequate and reveal no squamous intraepithelial lesions (or at most LSIL). If HSIL cytology or a high-grade colposcopic lesion is found during this time, a biopsy should be performed. In patients where HSIL cytology persists for 24 months but no high-grade lesion is identified on biopsy, a diagnostic excisional procedure is recommended. If colposcopy is inadequate, CIN 3 is specified on biopsy, or CIN 2 or CIN 3 persists for 24 months, a diagnostic excisional procedure is recommended. If CIN 2 is specified on biopsy, observation for 12 months using both cytology and colposcopy every 6 months is recommended. This guideline exists because CIN 2 has a higher regression rate and less risk of progression to cancer than CIN 3, especially in younger women. Once the patient has 2 consecutive negative results on cytology and no evidence of a colposcopic abnormality, co-testing is recommended a year later. If negative, a second co-test is recommended after three years. If either co-test is abnormal, colposcopy is recommended.  

For women 25 years old or older without special circumstances and with a HSIL Pap test result, expedited treatment is preferred if the immediate risk of CIN 3+ is ≥60% and acceptable if the immediate risk of CIN 3+ is between 25% and 60%. Expedited treatment is defined as treatment without a preceding colposcopic biopsy. Expedited treatment is preferred in women with HSIL and positive testing for HPV 16. Consideration of future pregnancy risks and shared decision-making should be considered when discussing expedited treatment.[21][22] (B3)

In women with HSIL, if the colposcopic exam is inadequate, a diagnostic excisional procedure is recommended. If the colposcopy is adequate and HSIL (CIN 2 or CIN 3) is confirmed on biopsy, ablation of the transformation zone or excision is considered acceptable. However, only a diagnostic excisional procedure is acceptable if the colposcopy is inadequate or the endocervical curettage shows a high-grade lesion.

Once the patient is treated, regardless of age, the recommended follow-up is HPV co-testing at 12 and 24 months post-treatment. If both are negative, she can be retested in 3 years. If this test is negative, she can return to routine screening for at least the next 20 years. An abnormal test should result in a colposcopy with endocervical sampling.[18][19](B3)

Pregnant women with HSIL cytology should not undergo excisional treatment; only colposcopy is acceptable. If a histologic diagnosis of a high-grade lesion is made, she may have additional cytologic and colposcopic exams up to every 12 weeks. If cytology results suggest invasive cancer or the colposcopic appearance of the lesion worsens, a biopsy is recommended. It is also considered acceptable to defer re-evaluation until the patient is at least 6 weeks postpartum.[21](B3)

Differential Diagnosis

Conditions that can be mistaken for HSIL on biopsy include early invasive cervical carcinoma, atrophy, squamous metaplasia, transitional metaplasia, and reactive atypia. 

Prognosis

HSILs are associated with persistent HPV infection and a greater risk of progression to invasive cancer, especially if the persistent infection is a high-risk genotype such as HPV 16 and/or HPV 18.