Endometrial Intraepithelial Neoplasia (EIN) is a precancerous condition involving the growth of abnormal cells in the uterine lining, known as the endometrium. While not cancer itself, EIN is a precursor because these cells can develop into endometrial cancer if left untreated. The diagnosis identifies specific changes in the endometrial glands that indicate an increased risk for malignancy.
Symptoms and Risk Factors Leading to Testing
The most common signal that prompts investigation for EIN is abnormal uterine bleeding. This can manifest as heavy menstrual periods, bleeding between cycles, or any bleeding after menopause. The underlying cause is a hormonal imbalance, specifically prolonged exposure to estrogen without sufficient counterbalancing from progesterone.
This state of “unopposed estrogen” is the primary risk factor for EIN. Conditions and life circumstances that contribute to this imbalance include:
- Obesity, as fat cells can produce estrogen.
- Polycystic ovary syndrome (PCOS), which can disrupt normal hormonal cycles.
- Never having been pregnant.
- Experiencing menopause at a later age.
- Using estrogen-only hormone replacement therapy without a progestin.
- Taking the medication tamoxifen, used in breast cancer treatment.
These factors create an environment where the endometrium is continuously stimulated to grow, increasing the chance of abnormal cell development.
The Diagnostic Procedures
To diagnose EIN, a doctor must obtain a tissue sample from the uterine lining for analysis. The most common initial procedure is an endometrial biopsy, performed in a doctor’s office. A thin, flexible tube is passed through the cervix into the uterus to suction a small amount of endometrial tissue for examination.
For a more comprehensive evaluation, a dilation and curettage (D&C) with hysteroscopy may be recommended. This is performed in a hospital or surgical center as an outpatient procedure. Hysteroscopy involves inserting a hysteroscope—a thin, lighted instrument with a camera—through the cervix to visually inspect the inside of the uterus and identify any suspicious areas.
Following the hysteroscopy, the D&C portion of the procedure is performed. The cervix is widened, or dilated, to allow a surgical instrument called a curette to be inserted. The curette is used to scrape away a larger sample of the endometrial lining than what is collected during an in-office biopsy. This provides more tissue for the pathologist to analyze for a definitive diagnosis.
Interpreting the Biopsy Results
The collected endometrial tissue is sent to a laboratory where a pathologist, a physician specializing in diagnosing diseases by examining tissue, analyzes it under a microscope. The pathologist looks for specific architectural and cellular changes in the endometrial glands to determine if EIN is present.
The diagnostic criteria for EIN include a change in the gland-to-stroma ratio, where glands become crowded and supportive tissue (stroma) is reduced. The pathologist also assesses the cells for cytologic atypia—abnormalities in cell size, shape, and appearance. To be classified as EIN, the lesion must be at least 1 millimeter in size and be distinguishable from the surrounding endometrium.
This diagnostic framework, the EIN system, has replaced older terminology like “endometrial hyperplasia.” The previous system categorized hyperplasia as simple or complex, with or without atypia. The EIN classification is favored because it more accurately predicts the risk of progression to cancer by distinguishing between benign hormonal effects and true precancerous lesions.
Next Steps After an EIN Diagnosis
After an EIN diagnosis, management focuses on preventing progression to endometrial cancer. The treatment path depends on the patient’s age and desire for future fertility. These factors determine whether the focus should be on preserving the uterus or on definitive treatment.
For individuals who wish to have children, a fertility-sparing approach is considered. This involves treatment with progestin-based therapies, which counteract estrogen’s effects and can reverse the abnormal cellular changes. Progestins can be administered through a hormonal intrauterine device (IUD) or oral medications, and this approach requires diligent follow-up with periodic biopsies.
For those who have completed childbearing or are postmenopausal, the standard recommendation is a hysterectomy, the surgical removal of the uterus. This procedure is a curative treatment for EIN, as it removes the tissue at risk of becoming cancerous. The fallopian tubes and sometimes the ovaries are removed at the same time, eliminating the risk of progression to cancer.