Soft Tissue Tumors

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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. Skin tag (acrochordon) clinical and histology

Benign Vascular & Neural - Vessel & Nerve Vibes

  • Infantile Hemangioma:
    • GLUT1+; most common tumor of infancy.
    • Phases: Proliferating (rapid growth, 0-1 yr), Involuting (slow regression). Infantile Hemangioma GLUT1 positive histology
  • 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.
    • Kaposi Sarcoma Lesions
  • 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.

Practice Questions: Soft Tissue Tumors

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A 7-year old boy presents with a right-sided hemangioma and left-sided focal seizures. The most likely diagnosis is:

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Flashcards: Soft Tissue Tumors

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Cutaneous horn can show features of _____ carcinoma at its base

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Cutaneous horn can show features of _____ carcinoma at its base

squamous cell

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