Molecular Particularity in Rare Tumour of Buttock: Case Report and Literature Review 145
cially in HSCTGR, has suggested a neural phenotype,
with the cells forming the rosettes being Leu-7, S-100,
and pgp 9.5 positive and the spindle cells usually being
negative [2,6,7]. The significance of the rosettes is un-
clear. However, cells forming rosettes have the ultra-
structural features of fibroblasts [6]. Moreover, they ap-
pear to be part of the neoplasm rather than a necrobiotic
granuloma-like response within the tumor [6]. Similar
appearing giant collagen-containing rosettes may be seen
in other mesenchymal tumors, including a neuroblas-
toma-like neurilemmoma, in which the rosettes are com-
prised of a core of collagen, flanked by small, round,
differentiated Schwann cells [6]. The microscopic dif-
ferential diagnoses of LGFMS include low-grade myxo-
fibrosarcoma, myxoid n eurofibroma, and myxo id solitary
fibrous tumor. Low-grade myxofibrosarcoma has more
cellular atypia and less swirling of tumor cells in a uni-
formly myxoid stroma. Myxoid neurofibroma shows
more wavy nuclei of the spindle cells and strong S-100
positivity. The osteoid, in rare cases of osteosarcoma,
may be confused for the collagen rosettes. Calcification
in the material and the surrounding marked nuclear
pleomorphism will help in settling the issue [2,8]. In the
original report by Lane et al., follow-up information was
available for 12 of the 19 patien ts, with a mean fo llow-up
period of 39 months [2,6]. Of the 12 patients, 7 were
treated with a simple local excision and 5 by a wide ex-
cision. Although one of the patients treated by simple
excision developed a local recurrence 20 months after the
initial surgery, none of the remaining patients had a re-
current or metastatic disease within the follow-up period.
Therefore, this lesion was considered to be a low-grade
sarcoma, and a wide surgical excision is the treatment of
choice [6]. Though the lesion appears bland in morphol-
ogy, long-term follow-up has revealed that it has a poten-
tial for metastasis, especially to the lungs [3,7,9]. Im-
proved recognition and treatment have improved the
prognosis of the lesion but, nevertheless, prolonged fol-
low-up is necessary. The discovery that LGFMS has a
specific translocation t(7, 16) (q33, p11), or in rare cases
t(11, 16) (p11, p11), has greatly facilitated the diagnosis
[10]. Through these translocations, the chimeric genes
FUS-CREB3L2 or FUS-CREB3L1, respectively, are
created. At the molecular level, the 5’-part of FUS, en-
coding a transactivation domain, is fused to the 3’-part of
CREB3L2 or CREB3L1, encoding a basic leucine zipper
(bZIP) DNA-binding domain [10]. A subset of LGFMS
cases expresses the FUS-CREB3L2 fusion transcript but
lacks the typical t (7, 16) and instead harbors a supernu-
merary ring chromosome, which may contain the fusion
gene, as the sole aberration [1,6]. Karyotypic information
on LGFMS reveals few other recurrent aberrations, sug-
gesting that the chromosomal translocations are tumori-
genic events.
In conclusion, we report a case of primary HSCT aris-
ing in the buttock harboring a molecular particularity
with a rare FUS-CREB3L1 fusion transcripts. The rec-
ognition of typical histological features and behavior of
HSCT of the soft tissue would be helpful for the man-
agement of patients, and detection of the characteristic
FUS-CREB3L2 fusion transcript or rarely FUS-CREB-
3L1 is necessary for the differential diagnosis of HSCT
involving unusual site. Therefore, an accurate tissue di-
agnosis with wide surgical excision and a close fol-
low-up are essential.
4. Acknowledgements
The authors thank Prof . J. M. Coindre for its opinion and
diagnostic follow-up study in molecular biology.
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