Fibroids are non-cancerous growths that develop in or on the muscular walls of the uterus. They are very common, with around 80% of women developing them at some point in their lives. But how do doctors know that fibroids are benign and not cancerous?
What are Fibroids?
Uterine fibroids, also known as myomas or leiomyomas, are abnormal growths that develop in the uterus. They are made up of smooth muscle cells and fibrous connective tissue. Fibroids can vary greatly in size, with some being too small to detect without imaging tests, while others can grow to the size of a melon or even larger.
Fibroids are classified into different types depending on their location. Intramural fibroids grow within the muscular uterine wall. Subserosal fibroids grow on the outside of the uterus. Submucosal fibroids grow just under the uterine lining. And pedunculated fibroids grow on stems that connect them to the uterus.
In many cases, fibroids do not cause any symptoms. But when they do, common symptoms can include:
- Heavy, prolonged menstrual bleeding
- Pelvic pain and pressure
- Frequent urination
- Pain during intercourse
- Lower back pain
- Reproductive problems, such as infertility, multiple miscarriages, or early labor
Fibroids tend to first develop during the reproductive years, when estrogen levels are higher, and typically start shrinking after menopause. Factors like family history, obesity, early onset of menstruation, and vitamin D deficiency can increase a woman’s risk of developing fibroids.
How Doctors Diagnose Fibroids
There are several different tests that doctors use to diagnose fibroids:
- Medical history and physical exam – Discussing symptoms and performing a pelvic exam can provide initial clues to fibroids.
- Imaging tests – Ultrasound, MRI, and CT scans can detect fibroids and map their location, number, and size.
- Laparoscopy – A minor surgical procedure to insert a thin scope into the abdomen and directly visualize the uterus and fibroids.
- Hysteroscopy – A scope inserted through the cervix to examine the uterine cavity and take samples of abnormal tissue.
- Biopsy – Removing small samples of uterine tissue to examine under a microscope. This can confirm a diagnosis of fibroids.
Once fibroids are detected, doctors will determine if they are the likely cause of any bothersome symptoms the woman is experiencing. From there, they can discuss options for managing troublesome fibroids, which range from medications to minimally invasive procedures to surgery in some cases.
Key Differences Between Fibroids and Cancer
Although both fibroids and uterine cancer affect the uterus, they have distinct differences that allow doctors to tell them apart:
| Fibroids | Uterine Cancer |
|---|---|
| Not cancerous or malignant | Cancerous and malignant |
| Grow slowly | Rapid, uncontrolled growth |
| Do not spread outside the uterus | Can invade and damage other pelvic tissues |
| Usually movable | Fixed tumor mass |
| Microscopically have normal cell patterns | Microscopically have abnormal cancer cells |
| Do not recur after surgical removal | Can recur after treatment |
| Not life-threatening | Potentially life-threatening |
The cells that make up uterine fibroids have a normal, non-cancerous appearance under a microscope. They do not have the abnormal structure and DNA mutations seen in cancerous cells. Additionally, fibroids do not invade into other tissues like malignancies do. They remain confined to distinct capsules within the uterus. These cellular differences allow doctors to confirm that fibroid growths are benign.
Imaging Tests
Imaging tests like ultrasound, MRI, and CT scans provide another way for doctors to differentiate fibroids from uterine cancer. These tests create detailed images that show the uterus and any abnormal growths inside and around it.
On imaging, fibroids have the following benign features:
- Round, smoothly marginated masses
- Multiple nodules clustered together
- Clear separation from surrounding tissues
- Organized whorled pattern internally
- No invasion into the endometrium or cervix
- Enhance normally after contrast dye
- No abnormal lymph nodes, fluid, or implants nearby
In contrast, uterine cancers appear imaging as irregular, poorly defined masses that can invade into nearby tissues. Lymph nodes, distant metastases, and abnormal fluid buildup may also be seen.
So imaging can reliably distinguish the appearance of harmless fibroids from that of cancerous growths involving the uterus.
Tissue Sampling
Examining uterine tissue samples under the microscope provides definitive confirmation that growths are fibroids and not cancer. This is done through procedures like hysteroscopy or surgical biopsy.
Fibroids show up on microscopic analysis as smooth muscle bundles with organized whorled patterns. The smooth muscle cells have regular, uniform nuclei. There are no abnormal cancer cells, mitotic figures, or invasion into surrounding tissues.
Meanwhile, cancerous uterine tissue shows disorganized architecture under the microscope, along with abnormal cancer cells. Special staining can highlight cancer cell features like hyperchromatic nuclei and high mitotic activity.
So microscopic analysis of tissue samples can reliably distinguish fibroids from uterine cancers based on cellular features and structure.
Molecular Testing
Newer molecular tests allow doctors to analyze genetic mutations and molecular biomarkers in uterine tissue samples. These can identify abnormalities that differentiate cancerous tissue from normal fibroid tissue at the DNA and protein levels.
For example, a test result showing mutations or abnormal expression of TP53, KRAS, PTEN or other cancer-related genes supports a diagnosis of uterine cancer rather than benign fibroids.
Risk Factors
Looking at a woman’s medical history and risk factors provides additional clues regarding whether uterine growths are likely to be fibroids or cancer.
Some key differences in risk factors include:
| Fibroids | Uterine Cancer |
|---|---|
| – Peak incidence age 30-50 | – Peak incidence after menopause |
| – No effect of oral contraceptives | – Reduced risk with oral contraceptives |
| – Pregnancy decreases risk | – Increased risk with early menarche, late menopause |
| – No known behavioral risks | – Increased risk with high BMI, hypertension |
| – No genetic predisposition | – Increased risk for Lynch syndrome |
Doctors can use these risk factor profiles to determine if a woman’s presentation is more consistent with expectations for fibroids or uterine cancer.
Monitoring for Changes
In cases where the initial workup is inconclusive, doctors may opt for careful monitoring rather than immediately doing more invasive procedures. This involves:
- Repeating pelvic exams at periodic intervals, such as every 3-6 months
- Following up with ultrasound or MRI scans to monitor for tumor growth
- Monitoring symptoms like abnormal bleeding that may signal problems
Fibroids that appear worrisome usually exhibit benign behavior over time. They do not grow rapidly or invade into other structures. Benign fibroids also remain stable or even shrink in response to hormonal medications.
On the other hand, cancers will often progress quickly, becoming larger and more invasive into surrounding tissues. New symptoms will also frequently develop with advancing cancer. So monitoring suspicious growths over time can sometimes provide definitive evidence of their benign nature.
Age Milestones
Doctors also take into account key age milestones that provide reassurance regarding fibroids.
For example, a woman over age 50 who has a stable uterine mass that has been unchanged for years is very unlikely to have cancer given she is postmenopausal. Cancer rates climb closer to menopause then start declining after age 60.
Likewise, a small stable uterine mass in a woman in her 20s that causes no symptoms is highly reassuring. Uterine cancers virtually never occur in this age group, while small asymptomatic fibroids are common.
Conclusion
In summary, although both fibroids and uterine cancer involve abnormal growths in the uterus, doctors can reliably tell them apart using a combination of tools:
- Microscopic analysis of tissue samples
- Detailed imaging tests like ultrasound, MRI, and CT scans
- Evaluating risk factors and clinical history
- Careful monitoring over time
The differences in cellular features and behavior allow fibroids to be definitively distinguished from malignant uterine cancers. Doctors can feel confident providing reassurance to patients that their bothersome fibroids are not cancerous.