Alveolar soft part sarcoma

Alveolar soft part sarcoma, abbreviated ASPS, is a rare malignant soft tissue lesion typically seen in younger individuals.

Alveolar soft part sarcoma
Diagnosis in short
ASPS. H&E stain.
LM	large cells (~30-50 μm) with abundant eosinophilic cytoplasm and an eccentric nucleus +/-nucleolus, arranged in nest/separated by thin septa - vaguely resembles alveoli (at low power)
LM DDx	alveolar rhabdomyosarcoma
Stains	PAS +ve (cytoplasm)
IHC	TFE3 +ve (suggestive of translocation)
Molecular	t(X;17)
Site	soft tissue - usu. head and neck
Prognosis	poor

General

• Adolescents/young adults.
• Children -- classically location: base of tongue and orbit.
• Typical indolent initially - ultimately a poor prognosis.

Microscopic

Features:

• Arranged in nest/separated by thin septa; vaguely resembles alveoli (at low power).
• Large cells (~30-50 μm) with abundant eosinophilic cytoplasm.
• An eccentric nucleus.
• +/-Nucleolus.

DDx:

• Rhabdomyosarcoma, alveolar - usu. does not have sheets of rhabdoid cells.

Images

• 

  ASPS - low mag. (WC/Nephron)

• 

  ASPS - intermed. mag. (WC/Nephron)

• 

  ASPS - very high mag. (WC/Nephron)

www:

• ASPS - PAS (webpathology.com).
• ASPS - low mag. (nih.gov).
• ASPS - high mag. (nih.gov).

Stains

• PAS +ve (cytoplasmic) - considered the most useful.
• PASD +ve (cytoplasmic).

IHC

• TFE3 +ve -- suggestive of characteristic translocation.
• Desmin ~ 50% of cases.

Others:

• EMA -ve.
• Cytokeratins -ve.
• HMB45 -ve.
• Melan‐A -ve.

Molecular

• t(X;17)(p11.2;q25).

Note:

• Same translocation may be seen in renal tumour with Xp11.2 translocation.

EM

• Distinctive membrane-bound intracytoplasmic crystal lattice with ~5 nm fibres spaced 10 nm apart.

Image:

• Distinctive crystal lattice in ASPS (nlm.nih.gov).

See also

• Soft tissue lesions.
• Head and neck pathology.