Retroperitoneal sarcoma

The symptoms, and why they arrive late

The first symptoms are not tumour symptoms. They are the symptoms of something taking up room and displacing what sits next to it, so nearly all of them can be mistaken for something far more common.

What comes up most often:

• An abdomen that grows in girth without weight gain, or a lump that can be felt and was not there before.
• Dull abdominal or lower back pain, poorly localised, that never quite settles.
• Fullness, or feeling full after very little food.
• Unexplained weight and appetite loss.
• Compression symptoms: swelling of one leg, pain running down the thigh, pins and needles or loss of strength, urinary discomfort.

Clinical presentation and size at diagnosis: Manual de sarcomas abdominales, Spanish Association of Surgeons (2026), epidemiology and radiological diagnosis chapters.

Many are found by accident

A share of these tumours turns up on a CT scan ordered for something else: renal colic, a pre-operative work-up, an injury. That incidental finding is good news, even when it does not feel like it, because it arrives before the symptoms do.

If a retroperitoneal mass has been found on a scan done for another reason, what happens next matters more than speed: it should be assessed by a unit experienced in sarcoma before anyone operates on it.

What must not be done before surgery

This is where a potentially curable disease is spoiled, almost always with good intentions.

A retroperitoneal sarcoma is not operated on without knowing what it is. The diagnosis is made with an image-guided core needle biopsy, and the needle track is chosen by the surgeon who will operate, because that track is removed later along with the tumour. The biopsy must never cross the peritoneal cavity: doing so can seed the peritoneum and turn a localised tumour into disseminated disease.

Nor is it acceptable to remove the mass “to see what it is”. An unplanned excision, without diagnosis or plan, leaves residual disease in thirty to fifty per cent of cases and forces a second operation that is worse than the first.

And any fat-containing retroperitoneal tumour needs MDM2 and CDK4 molecular testing. That is what separates a benign lipoma from a well-differentiated liposarcoma, and the two cannot be told apart by eye.

Biopsy rule and molecular testing: Margin Clear — Surgical Oncology Board Review, sarcoma section. Formal indication for percutaneous biopsy: Manual de sarcomas abdominales, Spanish Association of Surgeons (2026).

The subtype changes the whole plan

“Retroperitoneal sarcoma” is not one disease but several that share an address. The difference between them is not academic: it changes where the tumour comes back if it comes back, and it changes the prognosis.

The three seen most often:

• Well-differentiated liposarcoma: slow-growing and rarely spreads to other organs, but recurs locally very often. The problem is local, and it is long-term.
• Dedifferentiated liposarcoma: more aggressive, recurs locally more often and can also metastasise, most commonly to the lung.
• Leiomyosarcoma: behaves the other way round. Local control is good and the main risk is distant metastasis.

Five-year local recurrence and survival by subtype, in a series of 377 patients treated with extended resection (Gronchi et al., Annals of Surgical Oncology, 2015): well-differentiated liposarcoma, local recurrence 18% and survival 87%; dedifferentiated, local recurrence 44% and survival 54%; leiomyosarcoma, local recurrence 5%, metastasis 55% and survival 57%.

The operation: removing the compartment, not the lump

Surgery is the only treatment that cures a retroperitoneal sarcoma, and the first operation is the one that decides. This is not a tumour to be peeled away from its surroundings: the visible edge is not the real edge of the disease.

The international standard is en-bloc compartmental resection: the tumour is removed together with the organs and planes around it, even where they do not look invaded, so that it comes out whole and unopened. In retroperitoneal liposarcoma that often means taking the kidney on that side, a segment of colon, or the psoas muscle.

It sounds excessive and it is not: operating this way reduces local recurrence compared with simply removing the tumour. Even so, and even in experienced centres, between twenty and forty per cent of patients have a local recurrence within five years. It is the leading cause of death in this disease — more than metastasis.

Compartmental resection principle: Trans-Atlantic Australasian Retroperitoneal Sarcoma Working Group (Swallow et al., Annals of Surgical Oncology, 2021). Local recurrence in high-volume centres: Gronchi et al. (Annals of Surgery, 2016, 1,007 patients) and MacNeill et al. (2018).

Radiotherapy and systemic treatment

Radiotherapy before surgery was tested in a European randomised trial, STRASS. Across the trial population it did not improve abdominal recurrence-free survival, and its results admit different readings by subtype. That is precisely why no single rule fits everyone.

The indication is therefore decided in a multidisciplinary board and always on histology: a well-differentiated liposarcoma is not a dedifferentiated one, and neither is a leiomyosarcoma. Chemotherapy follows the same logic, and its role is limited and equally subtype-dependent.

STRASS: Bonvalot et al., Lancet Oncology, 2020.

Where you are operated on matters more than in almost any other surgery

A general surgeon sees a retroperitoneal sarcoma a handful of times in a whole career. A specialist unit sees them every week, and that is where the difference lies: in recognising the subtype before going in, in planning what is taken en bloc and what is reconstructed, and in not spending the one good opportunity, which is the first operation.

That is why European guidelines and the international reference group recommend these tumours be treated in high-volume centres with a sarcoma board, and why referral networks exist: CSUR in Spain and EURACAN across Europe.

At Hospital General Universitario Gregorio Marañón around fourteen retroperitoneal sarcomas are operated on each year, within the CSUR programme.

If you have already been operated on elsewhere and the tumour has come back, a specialist assessment is still worth having. Surgery for recurrence is harder, but it is done, and it is done with results.

Reference-centre treatment recommendations: TARPSWG and EURACAN, as set out in the guidelines of the Spanish Sarcoma Research Group (GEIS).

What this page does not do

This does not replace a consultation. In retroperitoneal sarcoma the decision depends on the subtype, the size, which structures sit around the tumour and your general condition, and none of those four can be read off a screen.

The figures here come from published series of hundreds of patients. They describe groups, not people. Where you fall within them is not something the number can tell you.