Histologic Types of Soft Tissue Sarcoma

Histologic Types of Soft Tissue Sarcoma

Prepared by Dr. Serdar DEMIROZ

Soft tissue sarcomas (STS) represent a diverse group of malignant mesenchymal tumors with distinct molecular, histologic, and clinical behaviours.
Advances in cytogenetic and molecular diagnostics—notably the detection of recurrent translocations (e.g., t(X;18), t(12;16)) and gene amplifications (MDM2, CDK4)—have transformed diagnosis, replacing purely morphologic classification with a genotype-driven approach.
Prognosis varies widely according to histologic grade, size, depth, and resectability, underscoring the importance of precise histopathologic and molecular diagnosis in both treatment planning and patient counselling.

1. Undifferentiated Pleomorphic Sarcoma (UPS)

Overview

• Formerly known as Malignant Fibrous Histiocytoma (MFH).
• Typically affects men > 50 years, often in proximal lower extremities, trunk, or retroperitoneum.
• Presents as a painless enlarging mass.

Pathology

• Marked cellular pleomorphism and high mitotic activity.
• Areas of necrosis common.
• No specific genetic driver, making it a diagnosis of exclusion after ruling out other sarcoma subtypes.

Treatment

• Wide excision with negative margins.
• Radiotherapy: routinely used pre- or postoperatively for local control.
• Chemotherapy: reserved for metastatic or high-risk cases; response modest.

Prognosis

• Metastatic pattern: lungs > bone > liver.
• Lymph node involvement uncommon.
• Adverse prognostic features: large size, deep location, and lymphovascular invasion.

2.Liposarcomas

Overview

• Second most common soft tissue sarcoma after UPS.
• Arises from adipocytic differentiation; MDM2 amplification is characteristic.
• MDM2 regulates p53, and its amplification suggests dedifferentiation.
• Atypical lipomatous tumors / well-differentiated liposarcomas resemble adipose tissue both grossly and radiographically (fat-like on MRI).

 a.Dedifferentiated Liposarcoma (DDLS)

• May arise from pre-existing atypical lipomatous tumors or occur de novo.
• MRI: heterogeneous non-fatty areas adjacent to lipomatous regions.
• Histology: high-grade spindle cell component with MDM2 & CDK4 amplification.
• Retroperitoneal DDLS can reach massive size at presentation.
• Treatment: wide excision; radiotherapy used for extremity/trunk lesions, rarely in retroperitoneum.
• Chemotherapy response: poor; MDM2 and CDK4 targeted therapies under study.

b. Myxoid Liposarcoma

• Affects adults aged 30–60 years.
• Characteristic t(12;16)(q13;p11) translocation → FUS-DDIT3 fusion.
• Round cell component indicates poor prognosis.
• Unique for metastasis beyond lungs → abdomen, pelvis, spine.
• Sensitive to radiotherapy and chemotherapy.

c. Pleomorphic Liposarcoma

• Rarest and most aggressive form (5–10% of liposarcomas).
• Typically in patients >60 years.
• Histologic confirmation requires lipoblastic differentiation.
• Prognosis: poor; chemotherapy may provide modest benefit.

3.Synovial Sarcoma

Overview

• Occurs in adolescents and young adults, typically near large joints (knee, ankle).
• Despite its name, does not arise from synovium.
• Histology: monophasic (spindle) or biphasic (spindle + epithelial).
• Cytogenetics: t(X;18)(p11.2;q11.2) → SS18-SSX1/SSX2 fusion.
• Mimics: epithelioid tumors or malignant peripheral nerve sheath tumors (MPNST).
• Treatment: wide resection + radiotherapy; highly chemosensitive.

4.Myxofibrosarcoma

Overview

• Previously grouped with UPS; incidence ~0.1/100,000.
• Occurs in older adults (6th–8th decade).
• Predominantly in lower limbs, occasionally trunk or neck.
• Microscopic “tail sign” on MRI represents fascial spread.
• High local recurrence risk due to infiltrative margins.
• 5-year survival ~77%.
• Treatment: wide excision + radiotherapy; chemotherapy for advanced disease.

5.Clear Cell Sarcoma

Overview

• Also known as malignant melanoma of soft tissue.
• Immunohistochemistry: HMB-45, Melan-A, S100 positive.
• t(12;22)(q13;q12) → EWSR1-ATF1 fusion in nearly all cases.
• May express BCL-2.
• High potential for lymph node metastasis → consider sentinel node evaluation.
• Often indolent for years → frequent diagnostic delay and unplanned excision.

6.Angiosarcoma

Overview

• Usually affects elderly (>60 years); commonly involves skin and superficial tissues.
• Highly aggressive, often multifocal.
• Markers: CD31, CD34, ERG positive.
• May respond to Pazopanib (VEGFR inhibitor) or PD-1 immunotherapy.
• Treatment: wide excision; reconstruction often needed.
• Prognosis: poor due to early dissemination.

7.Kaposi Sarcoma

Overview

• Vascular endothelial tumor with four clinical types:
  Classic (Mediterranean/Eastern European)
  Endemic (African, often in children)
  Iatrogenic (post-immunosuppression)
  AIDS-related
• Associated with HHV-8 infection.
• Presents as violaceous plaques, nodules, or macules—commonly on lower limbs.
• May mimic vascular insufficiency or venous stasis.
• Secondary malignancies (e.g., Non-Hodgkin lymphoma) in up to one-third.
• Treatment: depends on type and extent—surgery, radiotherapy, or chemotherapy.

8.Epithelioid Sarcoma

Overview

• Most common soft tissue sarcoma of the hand and forearm.
• Occurs in patients <40 years.
• Often slow-growing and misdiagnosed as a benign fibrous lesion.
• Radiographs: may show calcification or cortical erosion.
• High recurrence and pulmonary metastasis risk.
• INI1 (SMARCB1) loss is characteristic.
• Treatment: wide excision + radiotherapy.
• Prognosis: generally poor.

9.Dermatofibrosarcoma Protuberans (DFSP)

Overview

• Low-grade dermal fibroblastic tumor (~1% of soft tissue sarcomas).
• Common in young adults, often on trunk and proximal limbs.
• t(17;22) → COL1A1–PDGFB fusion.
• May show fibrosarcomatous transformation (high grade).
• Treatment: wide local excision or Mohs surgery.
• Imatinib effective for unresectable or metastatic disease.

10.Extraskeletal Ewing Sarcoma

Overview

• Rare; affects thigh and gluteal regions.
• Rapidly enlarging painful mass.
• Cytogenetics: t(11;22)(q24;q12) → EWS-FLI1 fusion.
• Treatment: multimodal—chemotherapy + surgery ± radiotherapy.
• Prognosis: better than skeletal form if localized.

11.Extraskeletal Osteosarcoma

Overview

• Extremely rare (<1% of STS), usually in older adults.
• Produces osteoid matrix visible as calcifications on X-ray.
• Histology: malignant cells producing osteoid without bone involvement.
• Treatment: surgical excision ± radiotherapy; chemotherapy poorly effective.
• Prognosis: generally poor.

12. Extraskeletal Myxoid Chondrosarcoma

Overview

• Occurs in older adults, typically lower extremities.
• Radiographs: calcifications suggest chondroid origin, though no true cartilage present.
• t(9;22)(q22;q12) or t(9;17)(q22;q11) translocations.
• Indolent growth, but high recurrence and metastasis (~50%).
• Treatment: wide excision + radiotherapy; limited chemo response.

13.Alveolar Soft Part Sarcoma

Overview

• Affects young women (<30 years); usually thigh or gluteal region.
• Histology: alveolar architecture; t(X;17)(p11;q25) translocation.
• Slow-growing but aggressive, with frequent metastases.
• Treatment: surgery + radiotherapy ± chemotherapy.
• Requires long-term surveillance.

14.Leiomyosarcoma

Overview

• Smooth muscle–derived malignant tumor.
• Predominantly affects retroperitoneum and abdomen, less often extremities.
• Venous origin (e.g., IVC) indicates poorer prognosis.
• Markers: SMA, desmin, h-caldesmon positive.
• Treatment: wide excision + radiotherapy.
• Metastatic in ~20% at diagnosis; chemotherapy has limited role.

15.Rhabdomyosarcoma

Overview

• Most common STS in children; originates from skeletal muscle precursors.
• Subtypes: embryonal, alveolar, pleomorphic.
• t(2;13) translocation typical of alveolar type.
• Embryonal form common <5 years; small round blue cell morphology.
• Lymph node metastasis relatively frequent.
• Treatment: multimodal (chemotherapy + surgery + radiotherapy).
• Adults respond poorly to chemotherapy.

16.Malignant Peripheral Nerve Sheath Tumor (MPNST)

Overview

• Often develops in patients with Neurofibromatosis type 1 (NF1).
• Transformation of pre-existing neurofibroma suspected.
• Pain and rapid growth in a known neurofibroma are classic warning signs.
• Imaging: PET-CT may help detect malignant transformation.
• Histology: high-grade spindle tumor, S-100 positive in ~50%.
• Prognosis: poor; 5-year survival 30–40%.
• Treatment: wide resection + radiotherapy; chemotherapy limited benefit.

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