Desmoplastic Small Round Cell Tumor (DSRCT), from the CureRays guide library.

Desmoplastic small round cell tumor is a rare, aggressive cancer that mostly strikes teenagers and young men, scattering tumors across the lining of the abdomen; because it spreads within the belly so widely, treatment is intensive and combines chemotherapy, surgery to remove as much tumor as possible, and radiation to the whole abdomen to control the microscopic disease left behind.

What it is.

Desmoplastic small round cell tumor (DSRCT) is a rare and aggressive soft-tissue sarcoma that occurs mostly in adolescents and young adults and affects males far more often than females. It belongs to the family of 'small round blue cell' tumors and is defined by a specific genetic change — a fusion of two genes called EWSR1 and WT1 — that can be confirmed on a biopsy and distinguishes it from other cancers it can resemble. DSRCT characteristically arises on the lining of the abdomen and pelvis (the peritoneum), where it tends to form not a single mass but many tumor nodules scattered across the abdominal surfaces, surrounded by dense scar-like tissue (the 'desmoplastic' part of its name). Because it grows in the spacious abdominal cavity, it often causes few symptoms until tumors are large or numerous, so many people have widespread disease in the abdomen, and sometimes spread to the liver, lungs, or lymph nodes, by the time it is found. Common symptoms include abdominal pain, swelling or a feeling of fullness, a palpable mass, and weight loss. DSRCT is a serious diagnosis, and no single treatment is enough on its own — it requires an intensive, coordinated combination of treatments. The standard approach uses aggressive chemotherapy to shrink the disease and treat tumor cells throughout the body, surgery to remove as much of the visible tumor as safely possible (often called aggressive cytoreduction or debulking), and radiation to the whole abdomen and pelvis to treat the microscopic disease that surgery cannot reach. Care at a center experienced with this rare cancer, ideally within a clinical trial, gives the best chance of the most effective combination.

How radiation treats it.

Radiation therapy treats desmoplastic small round cell tumor by delivering beams of energy that damage the DNA inside tumor cells so they can no longer grow and divide. Its role in DSRCT is shaped by the unusual way this cancer grows: rather than forming a single mass that a surgeon can cut out cleanly, it scatters many nodules across the lining of the abdomen and pelvis, leaving behind countless microscopic tumor cells on these surfaces even after the most aggressive surgery. Because those cells are spread over such a wide area, treating them requires radiation to the whole abdomen and pelvis — known as whole-abdominopelvic radiation — rather than a small, focused field. Given after chemotherapy and surgery have removed the bulk of disease, this whole-cavity treatment aims to sterilize the microscopic cells left across the peritoneal surfaces and lower the chance of the cancer regrowing inside the abdomen, which is where DSRCT most often comes back. Treating such a large volume is demanding, because the kidneys, liver, bowel, and bone marrow all lie within or near the field, so modern intensity-modulated techniques are used to shape the dose as evenly as possible across the target while sparing those organs and limiting side effects. Where bulkier disease remains after surgery, an additional focused boost of radiation can be directed there to improve control. Radiation is also used in a more targeted way for specific deposits outside the abdomen — for example, a spot in the lung or a lymph node — to control a limited area of spread or relieve symptoms. In all of these settings, radiation works hand in hand with chemotherapy and surgery; none alone is sufficient against this aggressive cancer, and the whole-abdominal radiation step is a key part of the standard combination that gives the best chance of controlling the disease.

The ways we can treat it.

Whole-abdominopelvic radiation (WAP-RT). Radiation is delivered across the entire abdominal and pelvic cavity to treat the microscopic tumor cells scattered over the peritoneal surfaces after surgery; modern intensity-modulated techniques shape the dose to cover this large area while sparing the kidneys, liver, and bowel as much as possible.

Intensity-modulated radiation (IMRT). Shaping many beams allows the large abdominal target to be treated more uniformly while reducing dose to the kidneys, liver, and bone marrow, lowering side effects from this demanding treatment.

Focal boost radiation. After whole-abdominal treatment, an extra dose can be directed at areas of bulkier residual disease to improve control where the most tumor remains.

Radiation to distant sites. Focused radiation can control specific deposits outside the abdomen — such as in the lung or a lymph node — to relieve symptoms or treat a limited area of spread.

Questions we hear often.

Why does treatment for DSRCT use radiation to the whole abdomen instead of just the tumor? Because of how this cancer grows. DSRCT doesn't form one neat mass — it scatters many tumor nodules across the lining of the abdomen and pelvis, and even the most thorough surgery leaves behind microscopic cells spread over those wide surfaces. A small, focused radiation field would miss most of them. Whole-abdominopelvic radiation treats the entire cavity to sterilize that scattered microscopic disease and lower the chance of the cancer regrowing inside the abdomen, which is where it most often returns. It is demanding to deliver because the kidneys, liver, and bowel sit within the field, so modern techniques are used to shape the dose and protect those organs as much as possible.

Why are so many different treatments needed? Because DSRCT is aggressive and widespread in the abdomen by the time it is usually found, and no single treatment can control it alone. Chemotherapy treats tumor cells throughout the body and shrinks the disease; surgery removes as much of the visible tumor as safely possible; and whole-abdominal radiation treats the microscopic cells left on surfaces surgery can't fully reach. Each step does something the others cannot, and they work best together. This is why care is coordinated by a team experienced with the disease, and why enrolling in a clinical trial — which may add newer targeted approaches to this backbone — is strongly encouraged.

Who tends to get DSRCT? DSRCT mainly affects adolescents and young adults, and it occurs much more often in males than in females. It is rare, and it is driven by a specific gene fusion (EWSR1-WT1) that is not inherited and not caused by anything a person did — it arises by chance in the tumor cells. Confirming that gene fusion on a biopsy is important because DSRCT can look like other 'small round cell' cancers under the microscope, and getting the diagnosis exactly right ensures the intensive, combined treatment this cancer requires is used from the start.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.