Retroperitoneal Sarcomas, Pelvic Sarcomas & Proton Beam Radiation with Aggressive Surgical Resection

Causes  |  Sympoms  |  Diagnosis  |  Treatment  |  Outlook  |  Next Steps

Retroperitoneal sarcomas (sarcomas found in the back of abdomen) and pelvis sarcomas are rare tumors that often return even after they’ve been removed. This is called local recurrence (“local” because the tumor reappears in the same location as the original cancer). Retroperitoneal and pelvic sarcomas have local recurrence rates of 50% or greater. The use of proton beam radiation therapy before surgery followed by aggressive surgical resection results in significantly reduced local recurrence rates and higher chances of cure for people with these types of tumors.

Key Facts

  • Local recurrence is the leading cause of death in patients with retroperitoneal and pelvic sarcomas.
  • Proton beam radiation therapy allows the delivery of higher doses of radiation to the tumor than standard radiation therapy.
  • The combination of proton beam radiation therapy and aggressive surgical resection leads to lower local recurrence rates.


Sarcomas are cancers within the connective tissue of the body. They can occur anywhere in the body, and there are over 100 different subtypes of sarcomas. Sarcomas in the retroperitoneal (back of abdomen) area and the pelvis are notable because their location makes them difficult to treat without risking damage to nearby important organs.

The majority of retroperitoneal and pelvic sarcomas are one of the following two subtypes:

  • Liposarcomas: tumors arising from fat
  • Leiomyosarcomas: tumors arising from smooth muscle

The remaining tumors include a large variety of other subtypes including solitary fibrous tumor and malignant peripheral nerve sheath tumor.

Each subtype of sarcoma has a unique tumor biology, radiological appearance, and clinical behavior. For example, in well-differentiated liposarcomas, chromosome 12q is often amplified resulting in overexpression of genes called MDM2 and CDK4. These tumors have a characteristic appearance on CT scans as large fatty tumors with internal septations (segments). As these well-differentiated liposarcomas enlarge, they can develop more solid areas in a process known as dedifferentiation.

Risk Factors

The vast majority of retroperitoneal and sarcoma patients do not have any obvious risk factors for their disease, although risk factors for sarcoma do exist. These include:

  • Prior radiation, which can result in a radiation-associated sarcoma. The frequency of radiation-associated sarcomas increases with dose and with the post‑radiation observation period.
  • Genetic disorders such as neurofibromatosis 1 (NF1). NF1 patients have about a 15% lifetime risk of developing a malignant peripheral nerve sheath tumor (MPNST).


Retroperitoneal and pelvic sarcomas usually do not cause any symptoms until they reach large sizes. As a result, the average size of tumors when they are discovered is often greater than 10-15 cm (4-6 inches).

When symptoms do occur, they can be caused by

  • The tumor pushing on bowel, leading to abdominal discomfort, early satiety, weight loss, or bowel obstruction
  • The tumor compressing the inferior vena cava or iliac veins, causing leg swelling
  • The tumor pinching nearby nerves, causing lower extremity pain or weakness.

In one study of 500 sarcoma patients, 80% of patients presented with an abdominal mass, 42% with lower extremity neurologic symptoms, and 37% with pain.


Because retroperitoneal and pelvic sarcomas are usually asymptomatic, they are often first identified when they become large enough that the patient or their healthcare provider can feel a mass in their abdomen, or they are discovered incidentally on radiological imaging for other purposes.

Imaging Tests

Once a sarcoma is suspected, a CT scan of the abdomen and pelvis should be obtained with intravenous contrast to fully evaluate the tumor and its proximity to the surrounding organs, vessels, and nerves. MRI may be of benefit in certain circumstances such as determining the proximity of a tumor to major nerves or in patients with a contraindication to CT scan intravenous contrast.

A minority (10-20%) of patients with retroperitoneal and pelvis sarcomas present with metastatic disease, meaning the tumor has spread to other parts of the body. The most common sites of spread are the lung and liver. Thus a chest CT should be obtained in addition to the abdomen/pelvis CT.


Biopsies involve removing a tiny sample of tumor so that it can be better identified and planned for. The role for image-guided biopsy of retroperitoneal tumors is somewhat controversial. The advantages of image-guided biopsy include the high likelihood of establishing a tissue diagnosis and the ability to give pre-operative treatment. Core needle biopsy of retroperitoneal and pelvis sarcomas will give a correct diagnosis of sarcoma in over 90% of cases, although there is lower accuracy in determining the correct histologic subtype and tumor grade. There are theoretical risks of needle track or intraperitoneal seeding of tumor as well as bleeding, but these risks can be minimized by using the proper route to access the tumor (specifically by avoiding an anterior transperitoneal approach).


Treating sarcomas typically involves surgery to remove the tumor. For most sarcomas, giving radiation therapy before (pre-operative) or after (post-operative) surgery has been proven to reduce the chance that the tumor returns--also known as local recurrence. For retroperitoneal and pelvic sarcomas, however, delivering adequate doses of radiation is difficult. This is because the tumors are generally large and sit close to radiation-sensitive organs like the kidney, liver, and small bowel. Advanced techniques like proton beam radiation therapy can help avoid this issue and make local recurrence less likely.

Surgery and Aggressive Surgical Resection

Complete resection (surgical removal) of the tumor is a requirement for potential cure of pelvis and retroperitoneal sarcomas. “Aggressive surgical resection” refers to the removal of the tumor along with nearby organs and tissues in an attempt to remove all gross and microscopic traces of disease. This approach to treatment has been advocated by several centers, however, the ability of aggressive resections to eradicate all microscopic disease, especially when some adjacent organs and structures such as the aorta or duodenum are not removed, has been questioned.

Pairing aggressive surgical resection with alternate radiation modalities such as proton beam radiation therapy helps remove those remaining traces of tumor, making it increasingly possible to effectively treat retroperitoneal and pelvic sarcomas.

Proton Beam Radiation Therapy

Proton beam radiation therapy allows the delivery of higher doses of radiation to the tumor than standard radiation therapy.

An initial study of preoperative proton beam radiation therapy combined with aggressive surgical resection showed a local recurrence rate of only 10%.   A subsequent study compared patients who received proton beam radiation therapy combined with aggressive surgical resection to patients who received surgery alone and found the 5-year local recurrence rates to be 9% for the combined therapy group versus 35% for the surgery alone group.  Subsequently, a multi-institution phase I clinical trial was performed of pre-operative proton beam radiation where the usual dose (50 Gy) of radiation was given to the entire tumor and a boost dose (63Gy) was given simultaneously to the posterior region, which is the source of most local recurrences. Patients then went on to surgical resection. The clinical trial found that this strategy was safe to perform. The phase II portion of this study was presented at the American Society of Clinical Oncology 2021 annual meeting. Sixty patients were enrolled in the study, the vast majority of patients tolerated treatment well, and local control results are pending but look promising. There are only about 3 dozen proton beam radiation centers in the United States. The closest one to Columbia University Irving Medical Center is the New York Proton Center, which opened in East Harlem in 2018 with an estimated cost of $330 million.


For patients with retroperitoneal and pelvic sarcomas, the initial treatment is the best chance at cure. Once local recurrence occurs after surgery and/or radiation, chances of cure decrease. The combination of preoperative proton beam radiation therapy and aggressive surgical resection may provide the best chance for cure.

Next Steps

Given the rarity of these tumors and the specialized, multi-disciplinary expertise required for treatment, patients with retroperitoneal and pelvis sarcoma are best evaluated and treated at an established sarcoma referral center.

If you or your loved one have been diagnosed with this type of sarcoma, the Sarcoma Care Program at Columbia can help. Our surgeons have the experience and expertise to bring you the best quality care, as safely as possible, and as part of the Herbert Irving Comprehensive Cancer Center, access to all the latest resources and options available. Our team features pioneers in the areas of surgical oncology and sarcoma care.

To make a surgical appointment with the Sarcoma Care Program, please call us at (212) 305-0273 today or request an appointment online today .