What is Endometrial Stromal Sarcoma (ESS)?
Also known as...
- ESS
- Uterine stromal sarcoma
Endometrial stromal sarcoma (ESS) is a rare type of sarcoma of the uterus or womb that develops from the connective tissue cells of the lining of the womb (endometrium). ESS accounts for less than 1% of all uterine malignancies.
How rare is it and who does it affect?
ESS accounts for less than 1% of all womb cancers. The incidence of ESS in the UK and US is relatively low. In the UK, it is estimated that less than 100 women are diagnosed with ESS each year. An incidence rate of 0.15 per 100,000 and is similar in the US.
ESS can occur at any age but most commonly affects women in their 40s and 50s. There are more premenopausal cases than for other uterine cancers. The exact cause of ESS is unknown, but it has been associated with certain risk factors such as a history of breast cancer, hormonal therapy, and hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome.
How we can help you

Clinical Trials
Helping you understand, find and navigate clinical trials as potential treatment options

Genetic Testing
Genomic testing designed for people living with a cancer diagnosis who want to understand their cancer in more detail to support decision making.
Frequently asked questions
What is a clinical trial?
A clinical trial is a type of research study that tests new medicines, treatments, or approaches to care. The goal is to find out if they are safe and effective for people.
Who can take part in a clinical trial?
Each trial has specific rules called “eligibility criteria.” These might include age, type of condition, stage of illness, or previous treatments. These criteria can be very detailed, meaning that even if a trial looks suitable for you on the face of it, you may not be able to take part due to some specific inclusion or exclusion criteria. Clinical trials also sometimes limit access to patients from particular locations and/or are open to a limited number of patients.
Do I have to pay to take part in a clinical trial?
Most trials are free to take part in. The study team usually covers the cost of the treatment being tested. Sometimes travel expenses may also be reimbursed.
How does RareCan make finding trials easier?
Publicly available clinical trial data is often complex, unreliable, or out of date. We maintain our own highly curated database of UK treatment trials. Instead of you spending hours deciphering medical jargon, our expert team does the heavy lifting. We review the complex eligibility criteria, create a shortlist of trials tailored to your diagnosis, and support you and your clinical team in making referrals. We also update your report periodically as your situation or the trial landscape changes.
When is a trial likely to be an option for me?
Clinical trials are usually considered when there is no standard treatment available. This can happen when you are first diagnosed (particularly with a later-stage or rare cancer) but is most common after you have already received the standard-of-care treatments for your cancer.
If I use RareCan’s trial service, am I committing to join a trial?
No. RareCan helps you find information about potentially suitable trials. You should always talk to your clinical team about whether any of the trials identified might be suitable, and your doctor will make a referral if appropriate. The trial team will then talk you through the trial in detail before you decide whether you would like to join or not. You will then go through detailed screening to see if you are suitable for the trial. Whether you join a trial is always your choice.
Will I definitely get the new treatment?
Not always. Some trials randomly assign participants to receive either the new treatment or the best available standard treatment. This helps researchers make fair comparisons.
Is joining a clinical trial safe?
Trials follow strict rules to protect participants. Safety is closely monitored, but all treatments can have risks. The research team will explain these clearly before you decide.
If I pay for a Personalised Trial Report or InsightDecode, am I guaranteed a spot on a trial?
No, we cannot guarantee you will be enrolled in a trial. We work alongside you and your clinical team to find the best potential options. However, trials have very strict and complex eligibility criteria. Some of these criteria can only be assessed during medical screening at the trial site itself. Additionally, trials have limited spaces, meaning they may close enrollment even if you are a perfect match.
Do RareCan reports contain information about trials outside the UK?
No. At RareCan we are focused on helping you find treatment options in the UK. We will be extending the service to residents of other countries soon, and will start offering reports that include international trials in due course, but currently we are focused on providing high quality, personalised information about treatment trials in the UK only.
Do RareCan reports contain every clinical trial that might be suitable for me?
Not every trial. Our reports focus on treatment trials and aim to highlight the most relevant options for you. There isn’t a single perfect, complete source of trial information, so while we work hard to keep our database up to date, it may not include every possible trial. Our reports are designed to support you and your clinical team in exploring potential next treatment options, but they should not be seen as a complete list.
What is the difference between the Personalised Trial Report and the InsightDecode service?
The Personalised Trial Report searches for trials based on your general clinical history and cancer type. The InsightDecode service goes a step further by using your existing genetic test results (such as a FoundationOne or Guardant360 report). We translate that complex genomic data into plain English and use your specific genetic mutations (biomarkers) to find highly targeted, precision medicine trials that standard searches might miss.
How do genetic tests help identify clinical trials?
Many modern cancer treatments are “targeted therapies.” This means the drug is designed to attack a specific genetic alteration driving your tumour’s growth. A genetic test maps out the DNA of your cancer. By knowing your exact genetic profile, we may be able to match you to cutting-edge clinical trials testing new drugs against those specific mutations.
Do I need to have a genetic test before I can use RareCan?
No. We can conduct a comprehensive search using your standard clinical history through our Personalised Trial Report. However, having genetic data often opens the door to more specific targeted therapy trials. If you haven’t had a genetic test yet, you can explore our private Insight genomic testing services to get a detailed profile of your tumour.
I already have a complex genomic report from my doctor. Can you help me understand it?
Yes. If you already have a genetic test report but aren’t sure what it means for your treatment options, our InsightDecode service is designed exactly for this. We will translate the heavy scientific jargon into a clear summary and use the data to search for targeted trials that match your genetic profile.
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RareCan has over 3,000 members, here’s what some of them say.
The voices and experiences from our RareCan members, shared to help others on their own cancer journey.

“I joined RareCan to support research into my extremely rare and highly aggressive subtype of uterine cancer.”
— Lindy
RareCan Member

“I joined RareCan to get action and support and research on rare cancers”
— Steve
RareCan Member

“I joined RareCan because they have the solution to the challenges faced within rare cancer research.”
— Dave
RareCan Member

“I joined RareCan as it may help other people in the future.”
— Wayne
RareCan Member

“If my husband was alive today, he would encourage people to take part in research as you never know if you will ever need it in the future.”




