Sir,
We report a case of a male patient who presented with a painless swelling in the abdomen
noticed 6 months back, with sudden increase in size over the past 3 months. On examination,
there was a firm swelling of size 8 cm × 6 cm in the left hypochondrium, in the intramuscular
plane. Contrast-enhanced computed tomography revealed a well-defined solid mass lesion
with central hypodensity and heterogeneously intense postcontrast enhancement within
the rectus abdominis muscle in the supraumbilical region. Imaging features suggested
the possibility of a neurogenic tumor. Fine-needle aspiration revealed loose aggregate
and dispersed large cells with eccentric nuclei, prominent nucleoli, and abundant
granular cytoplasm [Figure 1a] and [b]. Many bare nuclei were seen. With the differential diagnosis of alveolar soft-part
sarcoma (ASPS) and granular cell tumor, a wide excision was done to remove the tumor.
Figure 1: (a) Smear showing loose clusters of large cells with abundant granular cytoplasm
(H and E, ×10). (b) High-power image showing frayed cytoplasm and large nuclei with
nucleoli (H and E, ×40). (c) histology showing large cells in nests with delicate
septa (H and E, ×10); inset showing granular cytoplasm, large nuclei, and prominent
nucleoli (H and E, ×40). (d) Intracytoplasmic rod-like crystals (Periodic acid–Schiff
with diastase, ×40)
The specimen showed a circumscribed soft reddish-brown tumor of size 6.2 cm × 5.7
cm × 3.3 cm. Histology revealed large polygonal cells in nests and organoid pattern
with delicate septa. The cells had abundant eosinophilic granular cytoplasm, eccentric
round nuclei, and prominent nucleoli [Figure 1c]. Nuclear atypia, tumor giant cells, multinucleation, and extensive lymphovascular
emboli were present. Periodic acid–Schiff (PAS) and PAS with diastase revealed tumor
cells with intracellular crystalline material [Figure 1d]. The tumor sections were subjected to a panel of immunohistochemical markers including
vimentin, desmin, pancytokeratin, chromogranin, CD10, myogenin, NSE, S-100, and Ki-67.
The tumor cells were positive to vimentin [Figure 2a] and desmin [Figure 2b]. The other immunohistochemical markers were negative. These morphological and immunohistochemical
features favored the diagnosis of ASPS.
Figure 2: (a) Tumor cells showing positivity to vimentin (×40). (b) Tumor cells with
desmin positivity (×40)
Discussion
ASPS is a slow-growing malignant soft-tissue tumor of uncertain origin and usually
occurs in young adults. It accounts for 1% of all soft-tissue sarcomas [1]
[2] with female preponderance. It is seen in the deep soft tissues of thigh or buttock
in adults and the head and neck region, especially tongue and orbit, in children.[1]
[2] Jia et al. described ASPS on the abdominal wall in a 2-year-old child.[3]
Aspiration smears will show large dyscohesive monotonous cells, having abundant fine
vacuolated to granular cytoplasm and round nuclei with prominent nucleoli. Stripped
nuclei and fraying of the cytoplasmic margins are quite common. ASPS shows distinctive
histomorphology of organoid or nesting pattern at low magnification, separated by
delicate vasculature. Loss of cellular cohesion of the centrally located cells in
nests results in pseudoalveolar pattern.[1]
[4] The neoplastic cells show distinct cell borders, granular cytoplasm, and central
nuclei with prominent nucleoli. Multinucleation and atypia can be seen. Faint intracytoplasmic
rod-shaped inclusions and granules seen in hematoxylin and eosin stain; highlighted
by PAS stain after diastase digestion as rod like crystals is very characteristic.[1]
[2]
[4] The differentials to be considered are granular cell tumor, metastatic renal cell
carcinoma, and clear-cell sarcoma of soft parts [Table 1].[5]
[6]
Table 1
Diagnostic criteria to differentiate alveolar soft-part sarcoma and its mimics
|
Alveolar soft-part sarcoma
|
Clear cell sarcoma
|
Renal cell carcinoma
|
Granular cell tumor
|
IHC - Immunohistochemistry; + - Positive; - - Negative; TFE3 - Transcription factor
binding to IGHM enhancer3; HMB-45 - Human melanoma black; EMA - Epithelial membrane
antigen
|
Histology
|
Pseudo-alveolar pattern Granular cytoplasm
|
Alveolar pattern Clear cytoplasm
|
Alveolar pattern Clear cytoplasm
|
Sheets and nests
|
Dense granular cytoplasm
|
Periodic acid-Schiff stain
|
Intracytoplasmic rod-like crystals
|
Positive due to cytoplasmic glycogen
|
Positive due to cytoplasmic glycogen
|
Positive due to cytoplasmic phagolysosomes
|
Electron microscopy
|
Membrane bound rhomboid crystals
|
Melanosomes with barrel stave internal structure
|
Long microvilli and abundant cell junctions
|
Autophagic vacuoles
|
IHC
|
|
|
|
|
Vimentin
|
++
|
++
|
++
|
++
|
Desmin
|
+
|
-
|
-
|
-
|
TFE3
|
++
|
-
|
-
|
-
|
S-100
|
+/-
|
++
|
+/-
|
++
|
HMB-45
|
-
|
++
|
-
|
-
|
CD68
|
-
|
-
|
-
|
++
|
EMA
|
-
|
-
|
++
|
-
|
CD10
|
-
|
-
|
++
|
-
|
Molecular studies
|
der(17)t(X; 17)(p11;25) ASPSCR1-TFE3 fusion transcript
|
t(12;22)(q13;q12)
|
VHL gene mutation
|
t(12;22)(q13;q12)
|
ASPS demonstrates consistent strong nuclear staining to Transcription factor binding
to IGHM enhancer3 (TFE3), in addition to focal desmin and S-100 positivity. Electron
microscopy and cytogenetics further helps confirm the diagnosis, with distinctive
membrane-bound rhomboid or rectangular crystals, composed of a periodical lattice
work of rigid fibrils and ASPSCR1-TFE3 fusion transcript due to specific translocation
der(17)t(X; 17)(p11;25).[1]
Surgical resection with clear margins is the appropriate treatment plan for ASPS.
Chemotherapy and radiotherapy are under consideration to prevent local recurrence
or metastasis. Age at presentation, tumor size, and the presence of metastasis influence
the prognosis.[1]
[4]