Soft tissue tumor

Author: Mikael Häggström

Gross processing

• If it appears fatty, gross and evaluate as a lipomatous tumor.
  If it appears fatty, gross and evaluate as a lipomatous tumor.

Generally sample one slice per centimeter.

Evaluation

File:Histopathology of solitary fibrous tumor.png

A solitary fibrous tumor, an example of spindle cell tumor.

In case of spindle cell tumors (having elongated nuclei), the following features may help to roughly classify the tumor:

• Pointed on both ends: True fibroblastic tumors
• Pointed on one end and blunted on the other ("bullet-shaped"): Neural/nerve sheath tumors (see section below)
• Blunted on both ends ("cigar-shaped"): Smooth muscle tumor
• Triangular: Myofibroblastic

In uncertain cases, the following immunohistochemistry markers are usually helpful:

• CD34, indicating a solitary fibrous tumor
• S100, indicating a neural or nerve sheath tumor (see section below)
• Desmin, indicating a muscular tumor (skeletal muscle or Smooth muscle tumor)
• Beta catenin, indicating fibromatosis

At least in case of enlarged atypical nuclei, consider sarcoma as a differential diagnosis, and if unsure, have a low threshold for consulting with people with expertise in the matter, as the visual difference between benign and malignant spindle cells is relatively subtle. Relevant stains may include MDM2 and CDK4 for liposarcoma.

• Main features of liposarcoma:[2] - Spindle cells with enlarged, hyperchromatic nuclei. - Apparently univacuolated adipocytes (may look normal). - Lipoblasts (multivacuolated), but neither necessary nor sufficient for diagnosis.
  Main features of liposarcoma:
  - Spindle cells with enlarged, hyperchromatic nuclei.
  - Apparently univacuolated adipocytes (may look normal).
  - Lipoblasts (multivacuolated), but neither necessary nor sufficient for diagnosis.
• Leiomyosarcoma: Variable atypia, often with cytoplasmic vacuoles at both ends of nuclei, and frequent mitoses.[3]
  Leiomyosarcoma: Variable atypia, often with cytoplasmic vacuoles at both ends of nuclei, and frequent mitoses.

Neural or nerve sheath tumors

• Schwannoma, characterized by cellular Antoni A areas (top) and a loose paucicellular Antoni B areas (bottom).
  Schwannoma, characterized by cellular Antoni A areas (top) and a loose paucicellular Antoni B areas (bottom).
• Schwannoma is also characterized by Verocay bodies (one encircled), which are stripes of anuclear zones, separated by cellular palisades.
  Schwannoma is also characterized by Verocay bodies (one encircled), which are stripes of anuclear zones, separated by cellular palisades.
• Neurofibroma: A spindle cell lesion composed of slender fibroblast-like cells with storiform pattern and very low amount of stroma.
  Neurofibroma: A spindle cell lesion composed of slender fibroblast-like cells with storiform pattern and very low amount of stroma.
• In case of atypia, keep in mind that metastatic melanoma is generally also positive for S100.[1]
  In case of atypia, keep in mind that metastatic melanoma is generally also positive for S100.

Further information: Evaluation of suspected malignancies

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