Understanding Atypical Polypoid Adenomyoma (APA)

An atypical polypoid adenomyoma (APA) is a rare, non-cancerous growth that occurs in the lining of the uterus (endometrium). Because it contains “atypical” cells and shares some characteristics with uterine cancer, receiving this diagnosis can be frightening. However, APA is a distinct condition that is generally considered premalignant-associated—meaning it is not cancer itself, but it has an important association with coexisting or subsequently detected endometrial cancer ^[1][2].

What This Diagnosis Does and Does Not Mean

• It is not cancer: APA is a benign-appearing lesion, but a thorough specimen is needed to ensure no precancer or cancer is coexisting in the uterus.
• The evidence is limited: Because APA is rare, much of what we know comes from small observational studies rather than large clinical trials.

What is APA?

APA is described by doctors as a biphasic lesion, meaning it is made up of two different types of tissue working together ^[3].

• Atypical endometrioid glands: These are the “building blocks” of the uterine lining that have begun to grow in complex or unusual patterns ^[3].
• Fibromuscular stroma: These glands are embedded in a tough, muscle-like tissue rather than the soft tissue usually found in the uterine lining ^[3].
• Squamous morules: These are small, round clusters of cells that often appear within the glands. While they can occur in other lesions, they are a common feature that helps pathologists distinguish APA from other conditions ^[4][5].

Incidence and Rarity

If you feel like you haven’t heard of APA, it is because it is exceptionally rare. By late 2018, only 466 cases had been documented in medical literature worldwide ^[6]. Because it is so uncommon, it does not have a standard “incidence rate” (like 1 in 1,000 people). Instead, it is mostly identified in individual case reports or small clinical studies.

It most frequently affects women of childbearing age, though it can sometimes occur after menopause ^[7]. Because it is rare, your medical team may consult with a gynecologic pathologist—a specialist who focuses on female reproductive tissues—to ensure the diagnosis is accurate ^[4].

Common Symptoms and Presentation

Most women diagnosed with APA seek medical attention because of changes in their menstrual cycle or difficulties with reproduction. Typical presentations include:

• Abnormal Uterine Bleeding (AUB): This is the most common symptom, often manifesting as heavy periods (menorrhagia) or bleeding between periods ^[7][8].
• Infertility: Some women discover they have APA during a workup for difficulty getting pregnant ^[9].
• Incidental Findings: In some cases, there are no symptoms at all, and the lesion is found during a routine imaging or a procedure for an unrelated issue ^[7].

The growth is often found in the upper part of the uterus (fundus) or the lower uterine segment, as its location can vary from patient to patient, and can range in size from a few millimeters to several centimeters ^[3][7].

The Link Between APA and Cancer

One of the most important things to understand about APA is its relationship with endometrial cancer. While APA is not cancer, the two can sometimes “overlap” or happen at the same time:

• Coexistence: In various small retrospective studies, between 5.9% and 10.8% of women with APA were found to have concurrent endometrial cancer at the time of diagnosis ^[2][7].
• Progression: If the APA is treated conservatively, there is an uncertain risk it could progress to cancer later. Estimates for this risk vary in research—sometimes reported between 10% and 20%—but these figures come from small series with differing follow-up lengths, and a later cancer might sometimes be an unrecognized concurrent lesion rather than true transformation ^[10][11].
• Precursor signals: APA can also coexist with atypical hyperplasia (also called EIN), which is a known precancerous condition of the uterine lining ^[2].

Because of these risks, the primary goal of treatment is to ensure the lesion is adequately assessed, fully removed if fertility is desired, and closely monitored ^[2][12].

Why Diagnosis Can Be Challenging

Because APA contains muscle-like tissue, it can sometimes mimic the appearance of myoinvasive carcinoma (cancer that has grown into the uterine wall) ^[4]. To get the most accurate diagnosis, doctors prefer using hysteroscopy—a procedure where a small camera is inserted into the uterus—to see the lesion and remove it precisely, rather than a “blind” biopsy or D&C, which might miss parts of the growth ^[13][14]. Special laboratory stains (like p16 or SATB2) are sometimes used as adjuncts by pathologists to help confirm it is an APA rather than a more aggressive cancer ^[4][5].

Moving Toward Treatment

There is no single “standard” protocol for APA because it is so rare. Treatment is highly individualized based on whether you wish to have children in the future ^[2].

• Fertility-Sparing Care: For those who want to conceive, doctors may perform a complete hysteroscopic resection to remove the growth while leaving the uterus intact ^[13][2].
• Definitive Care: For those who have completed childbearing, a hysterectomy (removal of the uterus) is often a definitive option that removes the uterine site to prevent the condition from returning or progressing to cancer ^[2][15].

Regardless of the path you choose, long-term follow-up with regular biopsies is essential to ensure the lining of the uterus remains healthy ^[16][17].