Soft Tissue Tumors

Intro & Classification - Tissue Titans Intro

Soft Tissue Tumors (STT) are a diverse group of neoplasms arising from mesenchymal (non-epithelial, extraskeletal) tissues. They are primarily classified by their biological behavior and presumed cell of origin.

• Biological Behavior:
  • Benign: Localized, no metastasis.
  • Intermediate: Locally aggressive, rare metastasis.
  • Malignant (Sarcomas): Invasive, metastatic potential.
• Cell of Origin (Histogenetic Types):
  • Fibrous (e.g., Fibroma, Fibrosarcoma)
  • Adipose (e.g., Lipoma, Liposarcoma)
  • Vascular (e.g., Hemangioma, Angiosarcoma)
  • Neural (e.g., Neurofibroma, MPNST)
  • Muscle (Smooth & Skeletal) (e.g., Leiomyoma, Rhabdomyosarcoma)

⭐ Lipomas are the most common benign soft tissue tumors.

Benign Fibrous & Adipose - Friendly Fibro-Fats

• Dermatofibroma (Benign Fibrous Histiocytoma)
  • Firm papule/nodule, often on extremities; may be pigmented.
  • Fitzpatrick's sign (dimple sign): Lateral compression causes central depression. 📌 DF - Dimples Firmly.
  • Histology: Spindle cells in storiform ("cartwheel") pattern, Factor XIIIa positive.

  ⭐ Fitzpatrick's sign (dimpling on lateral compression) is characteristic of dermatofibroma.

• Acrochordon (Skin Tag)
  • Soft, flesh-colored or brown, pedunculated papule; often multiple.
  • Common in intertriginous areas (neck, axillae, groin, eyelids).
  • Associated with obesity, insulin resistance, pregnancy.
• Lipoma
  • Soft, mobile, lobulated, painless subcutaneous nodule; variable size.
  • Composed of mature adipocytes (fat cells).
  • Most common benign mesenchymal tumor.

Benign Vascular & Neural - Vessel & Nerve Vibes

• Infantile Hemangioma:
  • GLUT1+; most common tumor of infancy.
  • Phases: Proliferating (rapid growth, 0-1 yr), Involuting (slow regression).
• Cherry Angioma (Senile Hemangioma):
  • Common in adults, ↑ with age; bright red papules.
• Pyogenic Granuloma (Lobular Capillary Hemangioma):
  • Friable, red, rapidly growing papule; often post-traumatic.
  • Misnomer (not pyogenic/granuloma).

  ⭐ Pyogenic granuloma is a rapidly growing, friable papule often occurring at sites of minor trauma, and is histologically a lobular capillary hemangioma.

• Neurofibroma:
  • Soft, dermal nodule; "Buttonhole" sign.
  • Associated with NF1.
• Schwannoma (Neurilemmoma):
  • Encapsulated nerve sheath tumor.
  • Histology: Antoni A (Verocay bodies) & Antoni B areas.

Malignant Derm Sarcomas - Sarcoma Scaries

• Dermatofibrosarcoma Protuberans (DFSP)
  • Locally aggressive, indolent; firm plaque/nodule.
  • Micro: "Storiform" pattern; CD34+.
  • Genetics: t(17;22) → COL1A1-PDGFB fusion.
  • ⭐ > Dermatofibrosarcoma protuberans (DFSP) is characterized by the COL1A1-PDGFB gene fusion resulting from translocation t(17;22).
• Kaposi Sarcoma (KS)
  • HHV-8 driven vascular tumor. 📌 "Kaposi Hates HHV-8"
  • Types: Classic, Endemic, Iatrogenic, AIDS-related (aggressive).
  • Clinical: Violaceous patches, plaques, nodules; skin, mucosa, viscera.
  • 
• Angiosarcoma
  • Aggressive endothelial malignancy.
  • Elderly; scalp, face (head/neck).
  • Risks: Post-radiation; chronic lymphedema (Stewart-Treves syndrome).

High‑Yield Points - ⚡ Biggest Takeaways

• Dermatofibroma (Benign Fibrous Histiocytoma) presents with a positive dimple sign (Fitzpatrick's sign).
• Keloids characteristically grow beyond original wound margins; hypertrophic scars do not. Intralesional steroids are first-line therapy.
• Lipoma is the most common benign soft tissue tumor, composed of mature fat cells.
• Neurofibromas, often linked to Neurofibromatosis Type 1 (NF1), may exhibit the buttonhole sign.
• Dermatofibrosarcoma Protuberans (DFSP) is a locally aggressive sarcoma showing a storiform pattern and COL1A1-PDGFB fusion gene.
• Kaposi Sarcoma, an HHV-8 associated vascular tumor, is frequently seen in HIV/AIDS patients, presenting as purplish lesions.