Investigating Abnormal Bleeding and Diagnosis

When it comes to endometrial cancer, the most important thing to know is that your body often provides an early warning sign: abnormal uterine bleeding (AUB) ^[1]. For those who have already gone through menopause, any amount of bleeding—whether it is a full period, light spotting, or even a pink or brownish discharge—is considered postmenopausal bleeding (PMB) and must be evaluated by a doctor ^[2][3].

While most postmenopausal bleeding is caused by non-cancerous conditions, it is the primary symptom in about 90% of women diagnosed with endometrial cancer ^[4].

The Ultrasound: A Triage Tool

The first step in a diagnostic workup is often a transvaginal ultrasound (TVUS). This imaging test uses sound waves to measure the endometrial thickness (ET)—the “stripe” or width of your uterine lining ^[2].

• A thin lining: If your lining is 4 millimeters (mm) or thinner during an initial episode of bleeding and the doctor can see the entire lining clearly, the chance of it being cancer is less than 1% ^[2][5]. However, this is not a personal guarantee. If bleeding persists or returns, further tissue evaluation is required regardless of how thin the lining appeared ^[5].
• A thickened lining: If the lining is thicker than 4 mm, your doctor will recommend a tissue sample (biopsy) to look for cancer cells ^[2].
• Limits of ultrasound: An ultrasound is a screening tool, not a definitive diagnosis. It can sometimes be difficult to see the entire lining clearly if you have fibroids (benign muscle growths) or if the uterus is tilted ^[6]. If the doctor cannot see the entire lining clearly, a biopsy is necessary regardless of the measurement ^[7].

The “Blind” Office Biopsy

An endometrial biopsy is usually performed in the doctor’s office. A thin, flexible tube is inserted through the cervix to suction a small sample of the lining ^[8].

While this test is excellent at finding cancer that has spread across the entire lining (diffuse disease), it has a significant limitation: it is a “blind” procedure ^[9]. The doctor cannot see exactly where the tube is sampling. Because of this:

• The biopsy can miss focal disease—cancer that is only growing in one small spot or on a polyp (a small growth on a stalk) ^[9][10].
• Up to 31% of office biopsies come back as “insufficient tissue,” meaning the sample wasn’t large enough for the pathologist to give a clear answer ^[9].

Crucially, an “insufficient” or “inadequate” result is not the same as a “negative” result. It means the test did not work and must be followed up with a more definitive procedure ^[9].

When to Seek a Hysteroscopy

If your office biopsy is negative or insufficient, but your bleeding persists or happens again, you require an individualized gynecologic assessment. Most often, this means a hysteroscopy with directed sampling ^[2][11].

During a hysteroscopy, the doctor inserts a small camera through the cervix to look directly at the inside of the uterus ^[12]. This allows them to see exactly where any abnormal tissue is located and perform a directed biopsy, ensuring the sample comes from the most suspicious area ^[12]. This procedure is often combined with a dilation and curettage (D&C), where the lining is gently scraped to provide a more complete tissue sample for the lab ^[2].

Other Causes of Bleeding

If your tests come back negative for cancer, your doctor will look for other common causes of abnormal bleeding:

• Atrophy: The most common cause of postmenopausal bleeding (60–80% of cases) is simply the thinning and drying of the vaginal or uterine lining due to low estrogen ^[1][13].
• Polyps: Benign growths in the uterine cavity that can bleed ^[13].
• Endometrial Hyperplasia: A condition where the lining becomes too thick. Some types, like atypical hyperplasia (also called EIN), are considered “precancer” and require treatment to prevent them from turning into cancer ^[3][1].
• Fibroids or Adenomyosis: Benign conditions of the uterine muscle that can cause irregular bleeding ^[14].
• Tamoxifen Use: Patients taking tamoxifen for breast cancer may develop a thickened lining. Routine ultrasound screening for asymptomatic users is not generally recommended, but any abnormal bleeding or discharge should prompt immediate evaluation ^[15][16].