Retroperitoneal Sarcoma

Section: Surgical Oncology Curriculum: Curriculum, page 66

Definition

• Sarcoma are a rare and heterogenous group of malignant tumours of mesenchymal origi
• Retroperitoneal sarcomas arise in the retroperitoneum - a space posterior to the peritoneal cavity and anterior to the paraspinous musculature.
• They make up 10-15% of all sarcomas.

Clinical presentation

• Typically does not cause symptoms until the tumour is large enough to compress or invade surrounding anatomic structures.
  • Lower extremity oedema due to compression of venous structures.
  • Referred pain to groin from compression of nerves.
  • Bowel obstruction
  • Serous ascites due to portal venous compression.
• May have night sweats, flu-like symptoms etc.
• Average median size at diagnosis - 15cm
• When to suspect
  • Most patients with a retro-peritoneal, extra-visceral, unifocal soft tissue mass will have a sarcoma

Differential diagnosis

Malignant

• Paraganglionomas
• Schwanomma’s
• Lymphoma
• Testicular tumour metastasis
• Colorectal tumour metastasis to retroperitoneal lymph nodes.
• Adrenocortical cancer

Benign

• Retroperitoneal fibrosis
• TB
• Abscesses
• Haematoma
• Castleman disease (benign proliferation of cells within the lymph nodes and other lymphatic tissues)

Investigations

Imaging

• CT used more often than MRI (opposite to peripheral tumours)
• CT-PET is usually performed prior to radical resection.
• MRI can be performed to help with anatomical delineation OR evaluate liver lesions.
• If planning on taking out a kidney - should do a MAG3 of the other side to ensure its function is OK

Bloods

• FBC
• LDH - if elevated need to consider lymphoma
• AFP and bHCG - would raise suspicion for germ cell tumour.

Biopsy

• Image guided CT percutaneous biopsy - is mandatory if considering neoadjuvant therapy
• Traditionally biopsy has been omitted but now recommendation to biopsy all of them.
• Sarcoma service should dictate biopsy

Histology

• Most common histological subtypes are liposarcoma leiomyosarcoma, or undifferentiated soft tissue sarcoma.
• Liposarcoma
  • Well-differentiated liposarcoma - low metastatic potential but high rate of local recurrence. Low grade lesion
  • De-differentiated liposarcoma - high local recurrence rate with the ability to metastasis.
• Leiomyosarcoma
  • Generally arise from the IVC or its tributaries (renal vein, iliac vein etc) - can thus present with bilateral lower limb swelling.
  • Can metastasize easily to lungs and liver (probably because they are arising from a blood vessel)

Stage

• See Sarcoma
• As per AJCC 8th edition
• Of note tumour size is not a prognostic factor for retroperitoneal STS

Treatment

• Surgery
• Radiation therapy
• Chemotherapy is generally not used for patients with locoregional disease
  • Can be used for metastatic disease (Doxorubicin and Ifosfamide although mostly doesn’t respond)

Respectability criteria

• Assessing respectability
  • Patients must NOT have
    • Peritoneal implants (sarcomatosis)
    • Bilateral renal involvement
    • Extensive spine involvement
    • Extensive Mesenteric root involvement.
    • Extensive liver hilar involvement.
    • Extensive major vessel involvement.
• Borderline resectable disease
  • Patients with resectable disease who are anticipated preoperatively to have gross residual disease with immediate sսrgerу (R2 resection).
  • In most cases, the residual tumor frequently abuts structures or organs that cannot be easily or safely resected, such as major blood vessels.
• Unresectable or metastatic disease
  • Patients who do not meet the criteria for resectable or borderline resectable disease.
• Surgery for liposarcoma
  • You have to remove all of the retroperitoneal fat on the side of the tumour

Management

• Resectable
  • Surgery
    • Surgery with macroscopic complete resection provides the only opportunity for cure.
    • R1 resections as commonly achieved as Ro resections are often not achievable due anatomical constraints
  • Radiotherapy
    • No clear role for RT in majority of patients with resectable RPS
      • May be considered for patients with tumours known to be high risk of local recurrence
      • Can be given pre or post-operatively.
      • No evidence - 1x RCT which showed no difference
    • Neoadjuvant
      • Advantages
        • Less like to radiate the small bowel
        • Can reduce gross tumour volume and allow downstaging.
        • Can give higher doses to tumour field.
        • May reduce the risk of intra-peritoneal tumour dissemination
        • Low grade disease - more likely to have issues with local recurrence
          • High grade lesions should have upfront surgery because more likely to die from metastatic disease.
• Borderline resectable
  • Controversial
• Unresectable
  • Observation in indolent histolgies who are asymtomatic with limited disease burden e.g. well-differentiated liрοѕarϲοmа
  • Treatment
    • Systemic
      • Systemic treatment based on tumours histology
    • Surgery
      • Palliative resection can be considered if significant chance of improving quality of life
    • Radiation
      • Palliative radiation therapy (RТ) may be offered in select cases of unifocal or symptomatic disease

Targeted therapy

• Rarely used
• TKI’s like Imatinib and Sunitinib can be used for tumours with cKIT or PDGFR-alpha mutation.