SOFT TISSUE SARCOMAS PART 1

• Sarcomas constitute a heterogeneous group of rare solid tumors of mesenchymal cell origin with distinct clinical and pathologic features:
  • They are usually divided into two broad categories:
    • Sarcomas of soft tissues:
      • Fat, muscle, nerve and nerve sheath, blood vessels, and other connective tissues
    • Sarcomas of bone
• Sarcomas collectively account for:
  • Approximately 1% of all adult malignancies and 15% of pediatric malignancies
• In 2021:
  • An estimated 13,460 people will be diagnosed with soft tissue sarcoma (STS) in the United States (0.7% of all malignancies), with approximately 5350 deaths (0.9% of all cancer deaths)
• The true incidence of STS is underestimated:
  • Especially because a large proportion of patients with gastrointestinal stromal tumors (GISTs) may not have been included in tumor registry databases before 2001
• Prior radiation therapy (RT):
  • To the affected area is a risk factor for the development of STS
• More than 50 different histologic subtypes of STS have been identified
• Common subtypes of STS include:
  • Undifferentiated pleomorphic sarcoma (UPS)
  • GIST
  • Liposarcoma (LPS)
  • Leiomyosarcoma (LMS)
• The anatomic site of the primary disease:
  • Represents an important variable that influences treatment and outcome
• The most common primary sites include:
  • Extremities (43%)
  • Visceral (19%)
  • Retroperitoneum (15%)
  • The trunk (10%)
  • Head and neck (9%)
• STS most commonly metastasizes to:
  • The lungs
• Tumors arising in the abdominal cavity:
  • More commonly metastasize to the liver and peritoneum
• Rhabdomyosarcoma (RMS):
  • Is the most common STS of children and adolescents and is less common in adults
• Prior to initiation of treatment:
  • All patients should be evaluated and managed by a multidisciplinary team with extensive expertise and experience in the treatment of STS:
  • Because STS is rare and often complex, adherence to evidence-based recommendations is particularly important:
    • Analysis of data from 15,957 patients with STS in the National Cancer Database (NCDB):
      • Showed that NCCN Guidelines-adherent treatment was associated with improved survival outcomes
• Pathology of Soft Tissue Sarcomas – Biopsy
  • A pretreatment biopsy is highly preferred:
    • For the diagnosis and grading of STS
  • Biopsy should be performed by an experienced surgeon or radiologist:
    • Placed along the future resection axis:
      • With minimal dissection and careful attention to hemostasis
  • The goal of biopsy is to:
    • Establish the malignancy and provide a specific diagnosis where possible and a grade where appropriate or feasible
    • Recognizing that limited biopsy material may underestimate grade
    • It may be accomplished by open incisional or core needle technique:
      • Core needle biopsy is preferred
    • However, an open incisional biopsy may be considered by an experienced surgeon
    • In patients without a definitive diagnosis following initial biopsy due to limited sampling size:
      • Repeat image-guided core needle biopsy should be considered to make a diagnosis
    • Although fine-needle aspiration (FNA) is a convenient technique:
      • It can be difficult to make an accurate primary diagnosis with FNA alone due to small specimen size and is thus discouraged
      • FNA may be acceptable in select institutions with clinical and pathologic expertise
    • Endoscopic or needle biopsy may be indicated for deep thoracic, abdominal, or pelvic STS
• Pathologists with expertise in STS should review the pathologic assessment of biopsies and resected specimens:
  • Especially for initial histopathologic classification
  • Margins must be thoroughly evaluated in these specimens
  • Morphologic assessment based on microscopic examination of histologic sections:
    • Remains the gold standard of sarcoma diagnosis
• The differential diagnosis of a soft tissue mass includes:
  • Malignant lesions:
    • Such as primary or metastatic carcinoma, melanoma, or lymphoma
  • Desmoids
  • Benign lesions:
    • such as lipomas, lymphangiomas, leiomyomas, and neuromas
• However, since the identification of the histopathologic type of a sarcoma is often difficult, several ancillary techniques have been used as an adjunct to morphologic diagnosis:
  • These techniques include conventional cytogenetics, IHC, electron microscopy, and molecular genetic testing
  • Pathologists should have access to optimal cytogenetic and molecular diagnostic techniques
  • The results of appropriate ancillary studies used as an adjunct to morphologic diagnosis should be included in the pathology report
• The pathology report should include:
  • Specific details about the primary diagnosis (using standardized nomenclature according to the WHO Classification of STS tumor)
  • The organ and site of sarcoma
  • Depth, size, and histologic grade of the tumor
  • Presence or absence of necrosis
  • Status of excision margins and lymph nodes
  • Tumor, node, and metastasis (TNM) stage
  • Additional features such as:
    • Mitotic rate, presence or absence of vascular invasion and the type and extent of inflammatory infiltration

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