Understanding Endometrial Thickness and Its Association with Uterine Cancer

This article focuses on endometrial thickness as a risk factor for endometrial (uterine) cancer. The thickness of endometrial lining changes throughout the menstrual cycle and across different stages of a woman’s life. In this article, we discuss how these changes occur, what can go wrong and when to seek medical attention.

The endometrium, or uterine lining, is the tissue that lines the inside of the uterus sometimes referred to as the womb. Its primary function is to host the embryo during pregnancy. Throughout the menstrual cycle, the thickness of the endometrial lining changes, increasing with blood flow and nutrient supply in preparation for a potential pregnancy.

If pregnancy does not occur during the menstrual cycle, the endometrial lining sheds and leaves the body as menstrual blood. This thinning and thickening cycle repeats under the control of two hormones: estrogen and progesterone.

In addition to the menstrual cycle, the endometrial thickness also varies during different stages of a woman’s life, such as:

• From childhood to puberty
• From reproductive years to post-menopause

In reproductive-age, premenopausal women, the normal endometrial thickness at different phases of menstrual cycle are:

• Early phase of cycle (menstrual bleeding): The lining is expected to be thin.
• Proliferative phase: The endometrial thickness is roughly 4 to 8 mm; estrogen levels increase, causing thickening of the endometrial lining.
• Secretory phase: The endometrial thickness is roughly 8 to 14 mm (may be greater in some women); progesterone levels increase to maintain the endometrial thickness; a drop in progesterone levels signals the shedding of endometrial lining and initiation of menstruation (bleeding).

In postmenopausal women, the endometrium generally measures between 1 to 5 mm. This reduced thickness is a result of a significant decline in estrogen levels during menopause.

Other factors that may influence endometrial thickness include:

• Obesity
• Diabetes
• Use of estrogen hormone replacement therapy
• Use of Selective Estrogen Receptor Modulators (SERM), like Tamoxifen

Transvaginal ultrasound is the primary method for detecting abnormalities in the endometrial lining and measuring its thickness. The procedure usually starts with the insertion of an ultrasound probe into the vagina to get a clear view of the inside of the womb.

In complex cases, hysteroscopy serves as an alternative to transvaginal ultrasound. This technique is often performed alongside dilation and curettage (D&C) for biopsy. Your doctor may also recommend MRI (magnetic resonance imaging).

Estrogen and progesterone work together to keep endometrial lining at a healthy thickness. When there is too much estrogen, whether from within or outside the body, it disrupts this delicate balance.

Excess exposure to estrogen promotes continuous cell growth and endometrial thickening. Prolonged exposure to estrogen is also a major risk factor for endometrial/uterine cancer.

If the lining stays thick all the time, it can cause heavy and abnormal bleeding, which is not normal during or after menopause. This condition is known as endometrial hyperplasia. There are two types of endometrial hyperplasia:

• Typical hyperplasia: Benign overgrowth of endometrial cells causing thickening of the lining; can be treated by progestin in one of several forms.
• Atypical hyperplasia or endometrial intraepithelial neoplasia: This is not cancer yet, but it has a high risk of progressing into cancer if left untreated. About 30% of women with atypical hyperplasia develop endometrial cancer.

Endometrial polyps can also contribute to thickening. Polyps are benign overgrowth of endometrial cells that protrude into the womb cavity. People with polyps are also at risk for cancer if they have coexisting endometrial hyperplasia.

Additionally, women with Lynch syndrome or Cowden syndrome also face an increased risk for endometrial hyperplasia and endometrial/uterine cancer.

Abnormal vaginal bleeding is the most common sign of endometrial hyperplasia and endometrial/uterine cancer. Most women diagnosed with uterine cancer experience abnormal vaginal bleeding, making it one of the most common early warning signs of the disease. For women who have undergone menopause, any amount of bleeding is abnormal.

For younger individuals (under 55 years old) who have not gone through menopause, abnormal bleeding may include:

• Bleeding between menstrual cycles
• Bleeding after intercourse
• Prolonged menstrual bleeding
• Heavy menstrual bleeding

To diagnose endometrial hyperplasia and rule out cancer, doctors may recommend an endometrial biopsy to examine the tissue under a microscope. They may also suggest tests for biomarkers, but these are still experimental and not routinely performed.

If bleeding persists or returns within three to six months after a benign biopsy result, doctors will order further evaluation.

For those at high-risk of developing endometrial cancer, a total hysterectomy can be a definitive treatment for endometrial hyperplasia and a strategy to reduce cancer risk.