Now continuing with our “what you should expect” series in cervical cancer, in this section we are going to cover pathology of cervical malignancies. In order to treat cervical malignancies it is important that we understand what really goes on at cellular level.
We have described the anatomy, and histology of the cervix in previous article, and we know the normal cellular makeup of the cervix, the transformation zone and squamous metaplasia. Now we are all set to understand the abnormal findings i.e the pathology. This article also includes intraepithelial lesions.
What gives rise to cervical cancer in the first place?
Cervix consists mainly of epithelium, a few neuroectodermal cells (neuroendocrine, melanocytic cells) and stromal cells. As we know the transformation zone is covered in metaplastic squamous epithelium, whcih gives rise to squamous cell carcinomas. Within the cervical canal, lies coumnar cells, which give rise to adenocarcinoma. It must be noted that most cervical cancers arise from a premalignant lesion, which means that some changes occur within the cervix, which in the long run if not taken care of gives rise to a malignancy.
HPV(human papilloma virus) has been identified as the cause of majority of these premalignant changes which ultimately lead to cancer. HPV infections are likely to transform into a malignancy if the virus is of the high risk type i.e (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 73, and 82).
The usual picture of a patient with cervical cancer is most commonly irregular bleeding per vaginal or vaginal discharge. Patients undergo a per vaginal exam folowed by a pap smear(which will be discussed later). Initially the lesion is small in size and causes an erosive lesion within the cervix. The lesion the grows in size if left untreated to become ulcerated or exophytic with hardening of the cervix.
Sometimes the mass may be endophytic (i.e it grows within the walls of the cervix) and may not be visible or felt externally and may not be detected on a pap smear. When the cervix becomes large and bulky, greater than 6 cm in size it takes the shape of a barrel, hence the name ‘barrel shaped cervix’. This gross finding is usually seen in adenocarcinoma cervix.
After we understood about the gross picture of ca cervix, it is then important to understand the pathway of local extension.
Cervical lesions can move both sideways or downwards. It can move sideways to move the parametrium or move downwards to involve the vagina. From the parametrium it can move further laterally to involve the pelvic walls. In advanced cases the lesion may involve the urinary bladder anteriorly or the rectum posteriorly or both. In rare cases the lesion may invade upwards and involve the uterus and fallopian tubes.
It must be noted that the lesion involves the parametrium via lymphatics.
The gross aspect of the disease was not difficult to grasp wasn’t it? Now i’ll try to explain the microscopic aspects of the disease.
Squamous Intraepithelial Lesion–
It must be noted that intraepithelial lesions within the cervix is a common finding. Most of them are low grade, while the rest are high grade. These lesions are caused by the Human papilloma virus. The strains responsible for high grade lesions are 16, 18, 45, 31, 33, 52, 58, and 35. Of these 16 and 18 carry the highest risk of a high grade lesion and strains 6 and 11 are responsible for most low grade lesions.
Initially intraepithelial lesions of the cervix were classified into 3 groups cervical intraepithelial neoplasia (CIN)-1,2 and 3 and then last being invasive carcinoma.
After studying the nature of the Human Papilloma virus and its behavior it was agreed upon that the nomenclature changed from a three tired CIN system to a two tiered “low-grade squamous intraepithelial lesion” (LSIL) and “high-grade squamous intraepithelial lesion” (HSIL).
It can be seen in the diagram above that the two HPV proteins E6 and E7 inhibit the two tumor suppressor genes p53 and Retinoblastoma (Rb) gene gene respectively. Binding of E7 gene to Rb gene results in release of DNA replicating factor E2F which increases cell proliferation.
L-SIL corresponds histologically to CIN1 (dysplasia) or HPV related cellular changes without dysplasia. H-SIL corresponds histologically to CIN2 and CIN3.
It is recommended now that the LSIL and HSIL system be used instead of the CIN system.
What is LSIL?
LSIL is mostly flat and may rarely be exophytic, flat type being a dysplasia in the upper few layers of the epithelium or a cytopathic effect caused by HPV infection. Condylomata acunimatum has no dysplasia but has viral cytopathic effect. Even though condylomata is classified as an LSIL it has to be distinguised from a flat LSIL, but why?
Flat LSIL (more than 80%) are associated with high risk HPV strains and 12% transform into invasive cancer, but in condylomata acunimatum it is not so, it is caused by a low risk HPV strain and does not progress into invasive cancer. But for management purposes both fall under the spectrum of LSIL.
What cytopathic effect does HPV have on cervical cells?
Cytoplasmic halos, irregular nuclear membrane along with hyperchromatic staining of nuclei are assosciated with HPV infection, but it must be noted that these changes can also be seen in inflammatory conditions of the cervix.
Koilocytes are cells with changes as describe above- cytoplasmic halos, with irregular and coarse nuclei.
Hyperkeratosis is thickening of the stratum corneum layer of stratified squamous epithelium. The cells in condylomata acunimatum are arranged in papillary fronds, each frond having its own tiny blood vessel. Flat LSIL also shows koilocytes with dysplasia, present in the lower one third of the epithelium.
What is HSIL?
High grade squamous intraepithelial lesion shows middle to entire layers of stratified squamous epithelium being involved by dysplastic change. The cells in this lesion look much more omnious than LSIL cells. The HSIL cells show a change in polarity and other features such as nuclear atypia, increased nuclear cytoplasmic areas, increased mitoses and hyperchromasia.
HSIL lesion cover both CIN2 and CIN3 lesions. It is recommended that biopsy blocks are subjected to p16 testing. Stronger positivity for p16 is a feature of HSIL lesions. LSIL stains diffusely for p16.
Why is p16 stain used used??
p16 is a tumor suppressor that is coded by the CDKN2A gene. It acts by inhibiting CDK4-Cyclin D1 and CDK6-Cyclin D1 complexes. These complexes drive the cell cycle forward leading to cell proliferation. They act by phosphorylating(inhibiting) pRb thus releasing the E2F factor which promotes cell proliferation.
There is an inverse relation between p16 and pRb gene, and as we know that there is an inhibition of the pRb gene by the E7 molecule of the Human papilloma virus there is a rise in expression of the p16 gene. This causes increased p16 staining in HPV positive lesions.
p16 is useful in distinguishing HSIL from benign lesions but is not so useful in determining LSIL from benign lesions.
HPV testing in high risk females…Why is it important?
HPV testing has been an important part of screening guidelines in women older than 30 years and in those with abnormal cells on PAP smear. Abnormal cells of unknown significance in the presence of HPV have a higher chance of turning out to be an HSIL lesion.
We have discussed earlier that cervical cancer can be subdivided into various pathological subtypes.
The most common subtype of cervical cancer is squamous cell carcinoma, >99% of these are caused by HPV infection… Lets go into a bit of detail of Sqamous cell carcinoma and its subtypes.
- Superficially invasive squamous cell carcinoma (SISCC) – As per the FIGO guidelines SISCC was divided into 2 stages IA1 and 1A2. Both of them are 7 mm in transverse diameter and less than 3 mm and 3-5 mm in depth respectively. These patients can be managed more effectively with conservative methods (which will be discussed in another section) as they have low chance of lymph node metastases and recurrence.
How does squamous cell carcinoma look under a microscope?
Irregular nests of squamous epithelium with increased cytoplasmic keratinization.
They can be of the following subtypes-
- Keratinizing SCC- Here the cells are well differentiated and are arranged in nests, and sheets with cells occasionally arranged in dense, highly eosinophilic (they show an intense staining pattern) whorls called keratin pearls. The presence of even one keratin pearl is sufficient to diagnose a keratinizing SCC.
2.Non-keratinizong SCC– These consists of large cells, with indistinct borders and are also arranged in nests and cords. These do not have keratin pearls.
3.Basaloid variant-The cells in these variant are loosle attached, small and have scant cytoplasm. This variant is aggresive and fast growing hence necrosis is frequently observed.
4.Warty variant– this variant shows a picture similar to condylomata cunimatum and is less agressive as compared to the usual squamous carcinoma picture.
5.Papillary variant- This tumors are arranged in fronds, each having its own vessels and are line by highly dysplastic cells. Even grossly this tumor appears highly irregular with papillary projections. These tumors show a similarity to transitional cell carcinoma of the urinary bladder.
6.Verrucous carcinoma– This variant consists of well differentiated cells with similarities to condylomata acunimatum. These lack cellular atypia. They have smooth borders in comparison to conventional infiltrating borders of the convention squamous cell carcinoma. Local recurrences are common but lymph node and distant metastases are rare.
7.Lymphoepithelioma carcinoma- These tumors do not show features of regular squamous or adenocarcinoma. These tumors how a dense lymphocyte infiltrate containing plasma cells and eosinophils. This variant has a good prognosis as compared to conventional cervical carcinomas. In these tumors Epstein Barr virus maybe a causative agent although cases with HPV [positivity have been found.
8.Spindle cell carcinoma- These tumors have spindle shaped cells and can often be mistaken for a sarcoma. It may or may not have keratin,orepithelial pattern of cells. In this case immunohistochemical testing maybe necessary that helps to identify the epithelial origin of the tumor.
Histologic grade of tumor- The grade of a tumor depends on –> Keratin, nuclear atypia and mitotic activity.
Grade 1 —> Show keratinization, are well differentiated and show a low mitotic rate with minimal nuclear pleomorphism.
Grade 2—> Show lesser keratinization (individual cell keratinization), moderate mitotic mitotic activity and increased nuclear pleomorphism.
Grade 3—> Show very little to no keratinization, increased mitotic activity with marked nuclear pleomorphism.
Endocervical dysplasia is not a well defined entity. It is actually atypical hyperplasia of cervical glands with no specific cause or outcome. It is not a precursor to adenocarcinoma in situ.
Adenocarcinoma in situ-It is the precursor to invasive adenocarcinoma. They begin at the squamocolumnar junction and spread proximally. Cells here have typical malignant features such as hyperchromatic bizarre looking nuclei, multiple nuceloli and show pseudostratification. It is distinguishable from invasive adenocarcinoma due to maintenance of normal tissue architecture, absence of fibrous changes in the stroma (desmoplasia). No neoplastic glands are seen as usually seen in invasive adenocarcinoma.
Cone biopsy is a better way of detecting the invasiveness of such lesions as in cytology and biopsy invasiveness may not always be detectable.
Sometimes adenocarcinoma in situ (AIS) maybe confused with other benign lesions, such as–
- Inflammatory conditions–although these conditions may show similarity in cellular morphology to AIS, what distinguishes the two of them is that in inflammatory conditions the chromatin are more open and mitotic activity is much less as compared to AIS.
- Tuboendometroid metaplasia– It must be noted that most AIS too demonstrate HPV positivity and show positive staining for p16. Tuboendometroid metaplasia also show positivity for p16. The two of these can be distinguished from each other due to the fact that AIS show high Ki-67 index and is negative for Estrogen and progesterone receptors while these are positive in Tuboendometroid metaplasia.
Intestinal metaplasia of the cervix consisting of goblet cells, paneth cells and neuroendocrine cells is now considered as AIS. This metaplasia could also be a feature of metastases from an intestinal primary. Intestinal metaplasia is CK7 positive, CK20 negative, and p16 positive. This profile is different from an intestinal metastases.
Glandular malignancies are classified into the following–
2)Mucinous carcinoma-gastric, intestinal, signet cell type
8)adenocarcinoma mixed with neuroendocrine features
Early invasive adenocarcinoma– There is no proper definition as to which lesion can be classified as early invasive or microinvasive carcinoma as in Squamous cell carcinoma. Tumors invading upto depths less than 5 mm have also been found to metastasize to pelvic nodes although rare. The depth of invasion is measured from the basement membrane to the deepest point of invasion.
Invasive endocervical adenocarcinoma-These maybe well differentiated, moderately differentiated or poorly differentiated.
Well differentiated tumors, the glandular architecture shows cribriform picture and Mitotic activity is seen.
Moderately differentiated tumors, the glands are more irregular and show less than 50% of solid growth, in poorly differentiated the glands and cells look even more bizzre and have a greater than 50% solid component.
Even after treatment such as hysterectomy in 1A1 and 1A2 disease there is a small risk of lymph node metastases. This is mainly because depth of invasion is not always determined adequately, what may seem like a superficially invasive disease may actually be a deep invasion.
The ‘Silva system’ of classifying the lesions into risk groups has thus been developed, which omits depth of invasion from the classification system, although we wont be going into detail of this classification system.
Mucinous carcinoma–Intestinal type– As discussed earlier these malignancies resemble intestinal malignancies, primary cervical malignancies of intestinal type are differentiated from secondary intestinal malignancies if they CK7 positive and CK20 negative.
Villoglandular carcinoma– This is a rare tumor with a good prognosis. They are diagnosed based on a certain pathological criteria and are excluded if they do not fit this criteria. Grossly these tumors are friable, condylomatous or fungating. Microscopically they have mild to moderate nuclear atypia, with smooth infiltrating borders. Clear and serous cells should not be present. These tumors have a good prognosis and a lesser chance of lymph node involvement.
Endometroid carcinoma– These tumors have a cribriform, glandular pattern with malignant cellular morphology. Carcinoma of the endometrial lining needs to be ruled out in order to diagnose cervical endometroid carcinoma. True cervical endometroid carcinoma arise from cervical endometriosis and are HPV negative while the rest are positive.
Clear Cell carcinoma– These tumors are not linked to Diethyl stilbesterol (DES) . They have bimodal age incidence, i.e in 20s or in 60s. The tumor is polypoid or fungating. They have cells that contain abundant clear cytoplasm and contain glycogen and hyaline globules. They have similar survival to the usual ca cervix.
Serous cell carcinoma– These are agressive tumors and are said to be cervical when spread from the endometrium are excluded. They too have a bimodal age distribution. They have marked nuclear atypia and psammoma bodies maybe present.
Mesonephric carcinoma- These tumors arise from the remnants of the mesonephric duct that were left behind after embryonal development. These are lined by malignant cuboidal cells and are positice for CD10, PAX 8 and CA 125. They can be quiet aggressive but are very rare.
How can you tell an endometrial carcinoma from a cervical carcinoma?
These two type can be difficult to distinguish but Immunohistochemistry studies may help in distinguishing between the two. Endometrial carcinomas are usually positive for Estrogen receptors, vimentin and negative for CEA whereas cervical malignancies are negative for Estrogen receptors, vimentin and positive for CEA. In endometrial carcinomas p16 positivity may not always be present due to HPV. Aggressive tumors can also be p16 and are not linked to HPV positivity. In situ hybridisation of HPV virus can help in the diagnosis between the two.
This article covers the main pathologies related to cervical malignancies. There are other variants too but are rare. Now that we understand the basic pathology that underlies the disease we are in a better position to grasp cervical screening and management of premalignant lesions.
Management of premalignant lesions will be covered in further sections.