Natalie Casarotto is 30 years old, she presents at your request for follow up of her cervical screening test result. Natalie's cervical screening test taken 2 weeks ago has been reported: HPV 16 positive, cytology shows a possible high grade squamous intraepithelial lesion. Colposcopic examination and biopsy are recommended. Natalie has been asymptomatic and this is her first abnormal cervical screening test. She has not been vaccinated for HPV.
HPV is a DNA virus and there are approximately 100 different types of this virus.
The types of HPV can be divided into low and high risk. HPV 16, 18, 31 and 33 are more frequently associated with severe dysplasia and invasive cancers whereas types 6 and 11 are more frequently associated with genital warts.
Infection with the HPV virus is one of the most important risk factors for the development of cervical cancer. The HPV DNA has been found in 99% of invasive cervical tumours and is essential for the development and maintenance of the malignant phenotype.
The HPV virus, when it invades, results in episomal transcription of genes which encode E6 and E7 oncoproteins. These proteins block the action of tumour suppressor gene products. E6 binds to and degrades p53 whereas E7 binds to and degrades pRb. The consequence is unrestrained progression through the cell cycle hence leading to dysplastic changes in the epithelium.
If the HPV DNA integrates into the host genome, the progression from dysplasia to cancer is favoured.
CIN means cervical intraepithelial neoplasia. The classification system of CIN is based on the degree of cellular differentiation and stratification of the dysplastic cells within the epithelium. This classification of the histological abnormalities is made following histological sampling at the time of cervical screening test or colposcopy.
Classification:
Note - The diagnosis of CIN1, 2, or 3 is based on assessment of the epithelium and does not imply invasion. CIN 3 is still confined to the basement membrane.
Regression and Progression of CIN:
CIN 2 and 3 are managed by treatment. The management of CIN 1 continues to be the subject of debate. In women over 25 treatment is offered if the changes persist over 2 years but in younger women treatment may be deferred for longer due to the high rate of spontaneous regression. However, for women of any age some clinicians may choose to treat CIN 1 at the initial colposcopy visit depending on symptoms and patient preference.
There are a number of factors which can determine the rate of progression of disease, such as the viral subtype, host immunity, cigarette smoking, long term use of oral contraceptive pills and coexisting STIs.
The National Cervical Screening programme aims to decrease cervical cancer deaths. This is currently achieved by screening:
A cervical sample is collected by the clinician using a speculum and a brush to sample cells from the transformation zone. The sample is then sent to the laboratory where it is tested firstly for evidence of high risk HPV infection. If a high risk HPV type is detected then cytological assessment of the cervical cells is performed to look for dyskaryotic cells.
Women with normal cytology should have a repeat test in 12 months as they remain at increased risk while they are HPV positive.
Women with borderline or mild dyskaryosis should also be recalled for a repeat test in 12 months but if the changes persist at 12 months they should be referred for colposcopy.
Women with moderate or severe dyskaryosis, or women with possible invasive cancer or glandular neoplasia are referred for an urgent colposcopy. All women with persistent HPV infection for 2 years with normal cytology are also referred for colposcopy.
Cytology is far from a perfect test. A smear test may show a false positive due to inflammation or infection. False negatives can occur due to sampling or screening error. The sensitivity varies between 50% to 85%, but it is a cheap, non-invasive, reproducible test which has been shown to decrease cervical cancer deaths.
The introduction of HPV testing in conjunction with cytology has been shown to increase the sensitivity of the cervical screening programme to up to 95-100% (for CIN 2 or worse). However there has not yet been enough time to determine whether HPV primary screening decreases mortality from cervical cancer.
Colposcopy is a procedure performed to look at the cervix under magnification. A speculum is inserted and the cervix visualised using a colposcope. Acetic acid solution (vinegar) is placed on the cervix to stain abnormal areas white (this is referred to as aceto white changes) and iodine solution to stain normal cells brown. This allows a biopsy to be taken from any area of abnormality which is visible through the colposcope.
Aceto white change is caused by the higher nuclear density and increased nuclear protein in dysplastic cells. When they are exposed to weak acetic acid the extracellular proteins and cellular nuclei are coagulated and appear white. Normal cells have less nuclear protein and small nuclei and the changes are not visible on colposcopy.
The iodine solution is used to stain glycogen. Dysplastic tissue (and metaplastic tissue) lack glycogen and therefore does not take up iodine stain in the same way as mature squamous epithelium. These features allow the colposcopist to determine visually the likelyhood and extent of dysplasia and select the appropriate areas for biopsy.
Other features that can be seen on colposcopy that are associated with more severe dysplasia include abnormal blood vessels (e.g. punctation or mosaicism) and abnormal surface contour.
Biopsy is used to obtain tissue diagnosis. The histology allows the degree of dysplasia to be determined (e.g. CIN 1, 2 or 3). Knowledge of the histological changes allows appropriate treatment.
Biopsy and histology is an essential component of diagnosis. Cytology on its own without tissue histology is not diagnostic.
The aim of treatment is to remove the abnormal area within the cervical transformation zone and prevent progression to invasive cancer. This can be achieved with ablative or excisional procedures.
Ablative treatments:
These techniques destroy tissue. This means there is no specimen available for histological assessment. The entire area of abnormality must be visualised and the colposcopist must be confident that there is no invasive cancer. These techniques are less commonly used in modern practice.
Excisional treatments:
These techniques remove the abnormal tissue and allow histological assessment. The specimen obtained can be used to confirm the degree of dysplasia, that there is no invasive cancer, and that the excision margins are clear.
LLETZ and knife cone biopsy remove a cone shaped piece of tissue from the cervix. The amount of tissue removed is dependent on the size of the transformation zone, the extent of the visible abnormality, and whether the upper limit of the lesion can be seen.
LLETZ is currently the preferred treatment method because it can often be performed at the same visit as the initial colposcopy (known as "see and treat"). It is performed under local anaesthetic. A wire loop is used to excise the transformation zone. The specimen is sent for histological assessment. This approach has the advantages of only needing one visit, is well tolerated, has a high success rate (approximately 95% cure), and allows tissue diagnosis.
Complications of excisional treatment:
Following treatment women are followed up with "test of cure" which involves HPV testing and cytology at 6 months post treatment. If this is negative (HPV negative) they can return to routine recall. If it is positive they require continued colposcopy surveillance.
There are two HPV vaccines available - Cervarix (bivalent - HPV 16 and 18) and Gardasil (quadrivalent - HPV 6, 11, 16, 18). A newer nonavalent vaccine (Gardasil 9) which protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52 and 58 is now available and is the vaccine currently used in the Australian National Immunisation Program.
Gardasil 9 is predicted to prevent approximately 90% of cervical cancers (compared to 70% with quadrivalent vaccine). It also prevents genital warts (HPV 6 and 11) and other HPV related cancers (eg vulval, vaginal, anal, penile, and oropharyngeal).
The vaccine is most effective if given before exposure to HPV (i.e. before becoming sexually active). In Australia the vaccine is offered free to all children in year 7 at school (age 12-13). A two dose schedule is used (0 and 6-12 months).
Catch up vaccination is available for people up to 25 years of age who have not previously been vaccinated or completed the course.
The vaccine can still be given to people who have already been exposed to HPV or who have had treatment for CIN, however it will only provide protection against the HPV types that they have not yet been exposed to.
It is important to note that vaccination does not provide 100% protection against cervical cancer. Women who have been vaccinated still need to participate in cervical screening when they reach the appropriate age. However, vaccination is expected to significantly reduce the incidence of cervical cancer in the future.
Since the introduction of the HPV vaccination programme in Australia in 2007, there has been a dramatic reduction in genital warts in young people, and early evidence suggests reductions in high grade cervical abnormalities are also occurring.
The transformation zone is the area of the cervix where the columnar epithelium of the endocervix meets the squamous epithelium of the ectocervix.
Embryological development:
The cervix and upper vagina develop from the Mullerian ducts which are lined with columnar epithelium. The lower vagina develops from the urogenital sinus which is lined with squamous epithelium. During fetal life these two epithelial types meet at a junction called the original squamocolumnar junction which is usually located at the external os of the cervix.
Changes at puberty:
At puberty, under the influence of oestrogen, the cervix grows and everts. This causes the columnar epithelium from the endocervical canal to be exposed on the ectocervix. This is called an ectropion (or ectopy). The columnar epithelium is now exposed to the acidic environment of the vagina.
Squamous metaplasia:
Squamous metaplasia is the process by which the exposed columnar epithelium is replaced by squamous epithelium. This is a normal physiological process that occurs throughout a woman's life but is most active during puberty, pregnancy, and when using the oral contraceptive pill (times when oestrogen levels are high).
The area of the cervix where this metaplastic change is occurring is called the transformation zone. The transformation zone lies between the original squamocolumnar junction and the new squamocolumnar junction (where the columnar epithelium currently meets the squamous epithelium).
Importance of the transformation zone:
The transformation zone is important because:
The position of the transformation zone changes throughout a woman's life. In young women it is usually visible on the ectocervix. As women age and oestrogen levels fall (particularly after menopause), the cervix shrinks and the transformation zone moves up into the endocervical canal where it may not be fully visible at colposcopy. This can make both screening and colposcopy more difficult in older women.