Cervical transformation zone and cervical cancer
Most pre-malignant (not yet cancer) and malignant change in the cervix (the neck of the womb) arises at the transformation zone, where flat squamous cells meet tall columnar cells.
Remember
Most pre-malignant and malignant cervical change arises at the transformation zone, the join of the squamous and columnar linings, so a screening sample should include it.
The ectocervix is the part of the cervix that projects into the vagina, and its lining is stratified squamous epithelium (flat cells in several layers). The endocervix is the canal leading up towards the uterus, and it is lined by mucus-secreting columnar epithelium (tall cells).
The transformation zone is the join between these two linings, and it surrounds the external os (the opening of the canal into the vagina). Here columnar cells are replaced by squamous cells, a process called squamous metaplasia (one mature cell type turning into another), so the cells are constantly changing. Metaplasia itself is normal and does not mean that cancer is present.
Cells that are changing are particularly vulnerable when infection with high-risk human papillomavirus (HPV) persists, and this virus causes nearly all cervical cancers. The earliest abnormality is cervical intraepithelial neoplasia (CIN): surface cells grow abnormally, but the growth has not yet turned into cancer. Screening can detect CIN before cancer sets in.
That is why a screening sample, collected with a soft brush, should include cells from the transformation zone. In England the sample is tested first for high-risk HPV, and cytology, which means examining it under the microscope, is performed only if HPV is found.
Key facts
- Location
- the join between the squamous ectocervix and the columnar endocervix, around the external os
- Where change starts
- most pre-malignant and malignant cervical change arises at the transformation zone
- Why it is vulnerable
- squamous metaplasia means its cells are constantly changing, and the changing cells are particularly vulnerable to persistent high-risk HPV infection
- Main cause
- nearly all cervical cancers are caused by high-risk HPV infection
- Cell types
- with two cell types in the cervix, cancer can be a squamous cell carcinoma or an adenocarcinoma (a cancer of the mucus-producing glandular cells)
- Screening
- the sample, collected with a soft brush, should include cells from the transformation zone
Exam traps
- The whole ectocervix is not the area of greatest concern, which is where its squamous lining meets the endocervix.
- The endocervical canal can give rise to adenocarcinoma, a cancer of the mucus-producing cells, yet the canal as a whole is not the area of greatest concern; the join with the squamous lining is.
- The internal os, where the canal opens into the uterus, marks the boundary between cervix and uterus and is not a meeting of two types of lining, which is why it is not the usual site of pre-malignant change.
Read the full notes
Tested in 6 SimpleMed+ questions
Practice it in Reproductive System, with the answer and a full explanation after every question.
Practice these questions