How rare is spindle cell sarcoma?

In the UK and Europe the usual definition of a rare cancer is one that occurs in less than 6 people out of every 100,00 each year. Because there are around 200 rare cancers, this means that they make up about 24% (nearly a quarter) of all cancers.

According to data from Sarcoma UK, there are on average 173 cases of spindle cell sarcoma each year in England. This gives an incidence of 0.3 cases per 100,000 people. People affected by spindle cell sarcoma are usually older, typically in their late 60s and there are slightly more men affected than women. There are no significant risk factors for developing spindle cell sarcoma other than having previously been treated with radiotherapy for another cancer.

What is spindle cell sarcoma?

Spindle cell sarcomas are cancers that form from the connective tissues of the body such as muscle, fat, nerves, blood vessels and bone. They tend to form in the arms and legs often closer to the surface rather than in deeper tissues.

Unlike most sarcomas, spindle cell sarcoma is not a particular type, but a description of the shape of the cells that is used when nothing else fits – a “diagnosis of exclusion”.

When someone has developed a tumour it is very useful to understand exactly what type of cell it started in and whether it has any particular genetic mutations. This information will affect the type of treatment that is offered as different types of cancer respond differently to treatments.

As part of the diagnosis a small sample of tissue from the tumour is removed, (this is called a biopsy). The cells are studied under a microscope where they may be treated with special stains to see if they contain particular substances that are only made by certain types of cells. A histologist (scientist who studies cells) can tell from the shape, arrangement and ability of cells to absorb certain stains what type of cells they are. When cancer starts, it is usually in one, or at most a few cells. They start with the features of their original cell type, but the changes that allow them to start dividing uncontrollably also lead to changes that mean they stop looking like their original specialised cell and become “undifferentiated”. Sometimes these tests will allow the histologist to give a more specific diagnosis. For example a positive test for an “SS18” change is characteristic of a synovial sarcoma.

Undifferentiated cancers are named after the appearance of these unusual cells. In spindle cell sarcoma the main feature is that all, almost all, of the cells in the tumour are long and fairly thin – spindle shaped as in the sketch below.

They look a little like cells called fibroblasts that are responsible for making the material that holds the cells of connective tissue together.

Similar Sarcomas:
Spindle cell sarcoma is different from another undifferentiated sarcoma called undifferentiated pleomorphic sarcoma which has a more chaotic mix of cells with different shapes and sizes. There are also spindle cell forms of other types of sarcoma where the cells are spindle shaped, but still retain enough of their original character to be identified as a particular type. For example, spindle cell rhabdomyosarcoma is a sarcoma that starts in muscle cells and has spindle shaped cells.

In the nucleus of our cells is the molecule of inheritance, DNA. It looks like a twisted ladder where the order of the rungs acts as a simple alphabet, spelling out the instructions for everything that our cells make and do. A gene is a short section of DNA that contains the instructions for making one protein – proteins make up much of our bodies and have many other functions.

We can find the order of these letters by sequencing the DNA. Changes to the sequence are called mutations. Some mutations have little effect on us, but others can lead to cancer by changing the amount or activity of the proteins that are made.

Today, relatively quick and low cost DNA sequencing is allowing us to understand more about hard to define cancers and potentially identify features that allow us to treat specific changes that have occurred in the cells. Sometimes genetic analysis will identify mutated genes that will improve the diagnosis of the tumour to something more specific than spindle cell.

The most common mutations seen in spindle cell sarcoma are extra copies of some important genes. One called mdm2 reduces the cell’s ability to repair DNA damage, making extra mutations more likely. Other genes called CDK4, PDGFRa and KIT are all involved in stimulating or allowing cells to divide. All of these mutations have been seen in other types of cancers and are the target of a lot of research into new drugs.

What are the current treatment options for spindle cell sarcoma?

This is almost always the first option when treating spindle cell sarcomas. The surgeon will aim to remove the tumour along with a margin of healthy tissue, usually a few millimetres. This is to ensure that there are no cancer cells remaining that are not visible during surgery. The size of the margin will depend on the size and location of the tumour and how close it is to important nerves and blood vessels. If the tumour is in an arm or leg the surgeon will try to remove the tumour whilst making sure that the limb still works – a procedure called limb sparing surgery.

Treatment of the area with high energy radiation may be used to kill any remaining cancer cells after surgery. Alternatively radiotherapy may be used to reduce the size of a tumour before surgery or if a tumour can’t be removed.

Chemotherapy tends to be used if a spindle cell tumour has spread (become metastatic) rather than being the first choice of treatment. Treatment often involves drugs such as doxorubicin and ifosfamide which damage the DNA of dividing cells.

What current clinical trials are there for spindle cell sarcoma?

Information current as of: 30/05/23

There are currently no specific trials for spindle cell sarcoma, however there are trials where patients can join if their tumour has particular mutations that the trial drugs are targeted against. This includes a study at the Royal Marsden where a drug (BI907828) which targets tumours with extra copies of MDM2 is being tested alongside Ezabenlimab, which helps the immune system to attack cancer cells by blocking the cancer cells ability to switch off the immune response.

Where can I find support groups?

Sarcoma UK – The main UK sarcoma support site. 

Sarcoma support groups – A list of local and online groups for general sarcoma or more specific conditions. 

Awareness, events and symbols

All sarcomas have July as their awareness month.

The ribbon for sarcomas is yellow.