Endometrial Cancer: The 4 mm Thickness Rule and Treatment

Endometrial cancer, cancer of the lining of the uterus, is the fastest rising gynaecological cancer worldwide. Its main symptom is postmenopausal bleeding, and its first test is a transvaginal ultrasound: an endometrial thickness of 4 mm or less makes cancer very unlikely, while anything thicker in a woman who is bleeding needs a biopsy. Most cases are found early and carry a good prognosis.

Dr. Punyashree R M, a consultant gynaecological oncosurgeon and robotic surgeon at Fortis Hospital, CG Road, Bangalore, sets out who is at risk, how the diagnosis is made, how a precancerous lesion is managed in women trying to conceive, and how surgery and molecular classification now shape treatment. The other gynaecological cancers are summarised in the complete guide to gynaecological cancers.

Why endometrial cancer is rising so fast

Endometrial cancer is now diagnosed in about 420,000 women worldwide each year and causes close to 100,000 deaths. Dr. Punyashree said its global incidence has doubled in the last two decades and is expected to rise by another 50% by 2044.

The reasons are largely the ones driving non-communicable disease generally: changing lifestyles, fast food, obesity, and the rise of diabetes and hypertension, both of which are themselves risk factors for this cancer.

Endometrial cancer risk factors and protective factors

Endometrial cancer is driven chiefly by exposure to oestrogen that is not balanced by progesterone. When oestrogen stimulates the endometrium without progesterone to oppose it, the endometrial cells proliferate, can acquire mutations and become atypical, and can develop into endometrial intraepithelial neoplasia (EIN), a precancer of the endometrium that can progress to carcinoma.

Risk factors:

• High oestrogen exposure: early menarche, late menopause, nulliparity and anovulation
• Polycystic ovary syndrome (PCOS)
• Obesity, diabetes and hypertension
• Exogenous oestrogen therapy
• Tamoxifen therapy, commonly taken by women treated for breast cancer
• Age: more than 80% of women with endometrial cancer are postmenopausal
• Genetic predisposition, notably Lynch syndrome, an inherited condition that raises the risk of colorectal and endometrial cancer; a family history of colorectal or endometrial cancer should always be asked about

Protective factors:

• Combined oral contraceptive pills
• Progestogen-based contraception, such as the levonorgestrel intrauterine system (LNG-IUS)
• Pregnancy, during which the endometrium is protected from unopposed oestrogen
• Hysterectomy, which removes the endometrium altogether

PCOS: prevention starts with lifestyle

PCOS is one of the risk factors a clinician can influence early, and Dr. Punyashree treats it as a lifestyle disease. She once saw it mainly in women in their twenties to forties; she now sees it in girls as young as 10 to 12 in her outpatient clinic.

Her team usually does not start hormonal pills as first-line treatment. Instead, they explain the condition, often with a drawing: an egg grows in the ovary each month but is not released, it becomes a cyst at the surface, and repeated cycles leave multiple cysts. Patients are told what is disturbing the ovary's environment so that they understand why lifestyle matters. A healthy lifestyle, in her definition, covers diet and exercise, and also stress management and sleep.

Patients are given three to four months to make these changes, supported by antioxidant medication. Vitamin D and vitamin B12 deficiencies are checked at the first visit and corrected in parallel, and other hormonal causes are excluded. In her experience, 60 to 70% of patients report regular cycles at the end of three months.

Symptoms of endometrial cancer

The most common presenting symptom is postmenopausal bleeding. Dr. Punyashree estimated that 15 to 30% of postmenopausal bleeding is due to endometrial cancer; large pooled studies put the figure at about one in ten. Either way, the rest has benign causes, but every episode of postmenopausal bleeding must be evaluated.

Other symptoms include:

• Very heavy menstrual bleeding (menorrhagia) or bleeding between periods
• Abnormal vaginal discharge
• Pelvic pain or pain during intercourse
• Difficulty passing urine
• Unexplained weight loss
• A mass felt in the abdomen

Two further points are easily missed. A woman of reproductive age with heavy menstrual bleeding and a thickened endometrium on ultrasound needs an endometrial biopsy to rule out atypical cells. And a Pap smear can pick up endometrial cancer in 15 to 20% of cases: atypical glandular cells (AGC) on a Pap smear should raise suspicion of an endocervical lesion or an endometrial cancer.

How endometrial cancer is diagnosed: the 4 mm endometrial thickness rule

In a woman with postmenopausal bleeding, an endometrial thickness above 4 mm on transvaginal ultrasound means a biopsy; 4 mm or less makes cancer very unlikely.

Step 1: transvaginal ultrasound

The first investigation is a transvaginal ultrasound to measure endometrial thickness.

• 4 mm or less: cancer is very unlikely and further investigation may not be needed. Bleeding in this setting is more often due to an atrophic endometrium or endometritis.
• More than 4 mm in a woman with postmenopausal bleeding: a biopsy is required.

Step 2: endometrial biopsy

Hysteroscopy-guided biopsy, in which the uterine cavity is viewed directly and the abnormal area sampled, is the gold standard. A dilatation and curettage (D&C) or an outpatient pipelle biopsy, in which a thin tube draws a sample from the lining, are acceptable alternatives. Hysteroscopy is also covered on the hysteroscopy procedures cost page.

A thickened endometrium without bleeding

A postmenopausal woman with no bleeding but an endometrium thicker than 4 mm is a common referral. Dr. Punyashree's approach is to repeat the scan, particularly when the finding came from an abdominal ultrasound, to look for a polyp and to characterise the lesion: is the thickening uniform, and is there any invasion into the myometrium (the muscle wall)? If none of these features is present, the woman is kept under observation, with a repeat scan after three to six months to see whether the thickness is increasing or falling.

Step 3: imaging and the pathology report

After biopsy, contrast-enhanced MRI of the pelvis and abdomen, or PET-CT, is chosen according to whether the disease appears confined to the pelvis or may have spread beyond it.

The two most important findings in the pathology report are the type and the grade of the tumour. The most favourable is a grade 1 endometrioid adenocarcinoma, the most common type, which is treated successfully in most women.

Dr. Punyashree tailors imaging to that report:

• Endometrioid, grade 1, confined to the uterus on ultrasound: MRI of the abdomen and pelvis with contrast and diffusion-weighted imaging, which shows whether the tumour is invading the myometrium.
• Type 2 cancers, such as high-grade serous or clear cell carcinoma: a whole-body PET-CT, because these tumours spread quickly, including through the bloodstream to distant organs.

Where PET-CT is not available, she recommends MRI with contrast and diffusion-weighted imaging for suspected early disease, which defines the size of the tumour, myometrial invasion and involvement of the serosa (the outer surface of the uterus). For a type 2 cancer, MRI of the abdomen and pelvis can be combined with a CT scan of the chest to look for spread outside the abdomen.

Atypical endometrial hyperplasia (EIN) in IVF patients: the progestogen protocol

In a woman who wants to preserve fertility, EIN is treated with progestogens and repeat biopsies every three months until two in a row are clear. Endometrial hyperplasia with atypia, also called endometrial intraepithelial neoplasia (EIN), is a premalignant condition. Dr. Punyashree put its risk of progression to carcinoma at 25 to 50%.

She sees it most often in women undergoing IVF, who are exposed to high doses of exogenous hormones. Many of her referrals come from IVF centres that perform an endometrial biopsy just before embryo transfer, because the lining is thick, and find hyperplasia with atypia.

Her protocol for women who want to preserve fertility:

1. Treat with progestogens: high-dose oral progesterone together with an LNG-IUS.
2. Repeat the endometrial biopsy every three months.
3. When two consecutive biopsies are negative for EIN, return the patient to her fertility specialist for embryo transfer.
4. Once she has completed her family, perform a hysterectomy, because the risk of progression or recurrence persists.

Hormone therapy is also used for women with endometrial cancer who are unfit for surgery or who want to preserve fertility.

Endometrial cancer surgery and staging

Surgery is the main treatment for endometrial cancer, and minimally invasive surgery, laparoscopic or robotic, is the gold standard. Endometrial cancer is staged with the 2023 FIGO system, which in simple terms asks whether the cancer is confined to the endometrium, has reached the myometrium, has spread outside the uterus, or has spread distantly.

Treatment is primarily surgical staging:

• Stage 1, type 1 tumours: extrafascial hysterectomy.
• Spread to the cervix: hysterectomy, extended to a modified radical hysterectomy only where needed to obtain clear margins, with pelvic lymph node dissection and para-aortic lymph node dissection from level 1 to level 4, that is, up to the left renal vein.

Sentinel lymph node mapping, which removes only the first node draining the tumour, is used in early disease; the technique is described in the complete guide. Once the final pathology report is available, the team decides on adjuvant radiation or chemotherapy, given to reduce recurrence and improve overall survival.

Endometrial cancer molecular classification: how it guides treatment

Molecular profiling now determines much of the treatment plan. In Dr. Punyashree's practice, every patient with endometrial cancer should undergo molecular profiling, which places the tumour in one of four molecular groups: POLE-mutated, mismatch repair deficient, p53-abnormal, and no specific molecular profile.

The group can override the grade:

• POLE-mutated: the prognosis is good even for a high-grade tumour. She would not escalate to multiple treatment modalities; surgery, with radiation where indicated, would suffice.
• p53-abnormal: the patient must receive chemotherapy on schedule, all six cycles, with adjuvant radiation added where needed to reduce recurrence and improve overall survival.

Hormone therapy is guided by oestrogen and progesterone receptor status, but it is not commonly used across endometrial cancers as a whole. Targeted therapies are being studied and are given to selected patients, in recurrent disease, unusual tumour types or as maintenance. Where access is limited, Dr. Punyashree's view is that conventional treatment is good enough, provided the patient can be followed closely so that any recurrence is detected early and treated. Targeted maintenance therapy is a good choice for a defined subset of patients, not for everyone.

Endometrial cancer survival and prognosis

The prognosis of endometrial cancer is good: about 80% of women survive five years, and survival depends heavily on the stage at diagnosis. The adverse prognostic features are advanced age, grade 3 tumours, type 2 histology, deep myometrial invasion, lymphovascular space invasion (LVSI, tumour cells inside small blood or lymph vessels), lymph node involvement and distant metastases. Most of these reflect the stage of the disease, which is why investigating every episode of postmenopausal bleeding promptly makes such a difference.

Dr. Punyashree's answers on imaging without PET-CT and on molecular profiling where access is limited are on the Live Discussion page. Ovarian cancer, which shares several risk factors with endometrial cancer, is covered in early ovarian cancer symptoms and fertility-sparing surgery. Dr. Punyashree's profile is at Dr. Punyashree R M.