A doctor writes: cervical and endometrial cancers are two distinct diseases
Dr Muiris Houston explains differences in the detection, investigation and treatment of the cancers
While screening for cervical cancer is well established, there is no screening test for endometrial cancer. It can only be diagnosed after a woman develops symptoms. Photograph: Getty Images
It has emerged that one of the 221 women caught up in the CervicalCheck controversy actually had endometrial cancer. Cervical and endometrial cancers have a different biology and are identified in different ways.
The uterus (womb) has two major parts: the body of the uterus and the neck or cervix, which is situated below the uterine body and above the vagina.
While part of the same organ, the two structures have very different linings. The body of the uterus is lined with glandular cells; the neck of the womb is lined by squamous cells. Cancer of the body of the uterus is called endometrial cancer, and emerges from the glandular cells. It is known as adenocarcinoma. Cancer of the neck is called cervical cancer and usually develops from the squamous cell lining. It is called squamous cell carcinoma.
A small number of cervical cancers (10 to 15 per cent) are adenocarcinomas. But these cervical adenocarcinomas have a different appearance to endometrial adenocarcinomas when looked at under a microscope. They are two distinct diseases.
Therefore, cervical and endometrial cancers have a different biology and are detected, investigated and treated differently. While screening for cervical cancer is well established, there is no screening test for endometrial cancer. It can only be diagnosed after a woman develops symptoms. The primary symptom that suggests a woman may have endometrial cancer is the development of postmenopausal vaginal bleeding. It triggers an investigation called dilatation and curettage (D&C), during which scrapings of cells and a biopsy of any suspicious area is carried out.
Cervical cancer may be diagnosed before it causes symptoms. The cells at the neck of the womb undergo precancerous changes. By sampling these cells using a Pap smear test it is possible to pick up indicators of precancerous lesions or early-stage cancers. Such a screening test is not diagnostic but it identifies a subgroup of women who are at increased risk of disease.
A smear showing a high-grade squamous lesion will prompt a further investigation called a colposcopy (the direct visual examination of cervix). This does not look at the endometrium so is not an examination for endometrial cancer. A D&C and a colposcopy are two distinct and different investigations.
An area called the transformation zone is located at the middle of the cervix. It is the junction where glandular and squamous epithelium meet. Most cervical cancers arise from here and smears are targeted at sampling this area. However, contrary to some recent statements, the transformation zone has no relevance to endometrial cancer.
While it is possible for an endometrial cancer to spread downwards to involve the cervix (a stage 2 endometrial cancer) it is still an endometrial cancer, and not a cervical cancer.
We now know that at least one of the 221 CervicalCheck women had endometrial cancer and not cervical cancer. This reflects an administrative misclassification rather than a clinical error.
The reality is that a smear test is not designed to detect endometrial cancer. It is a screening test – not a diagnostic one – and one for a different disease. CervicalCheck continues to offer a reliable screening service for cancer of the cervix. It deserves the continued support of women invited to attend for screening.