Indian Journal of Pathology and Microbiology

: 2019  |  Volume : 62  |  Issue : 4  |  Page : 643--645

Recurrent monophasic synovial sarcoma in a child

Priyanka Maity Chaudhuri, Nelofar Islam, Mou Das, Uttara Chatterjee, Chhanda Datta 
 Department of Pathology, IPGME and R, Kolkata, West Bengal, India

Correspondence Address:
Uttara Chatterjee
Department of Pathology, IPGME and R, Kolkata, West Bengal

How to cite this article:
Chaudhuri PM, Islam N, Das M, Chatterjee U, Datta C. Recurrent monophasic synovial sarcoma in a child.Indian J Pathol Microbiol 2019;62:643-645

How to cite this URL:
Chaudhuri PM, Islam N, Das M, Chatterjee U, Datta C. Recurrent monophasic synovial sarcoma in a child. Indian J Pathol Microbiol [serial online] 2019 [cited 2021 Jun 20 ];62:643-645
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Synovial sarcoma (SS) is the most common non -habdomyosarcomatous sarcoma in children.[1] Usually found in adolescents and young adults, it is rare below the age of 2 years, with only a handful of cases describing this entity in infants.[2],[3],[4] It commonly occurs around the knee joint. The histomorphology of monophasic synovial sarcoma (MSS) overlaps with that of fibrosarcoma and malignant peripheral nerve sheath tumor (MPNST). Infantile fibrosarcoma (IFS) is a distinct entity seen in infants which shares similar histological features with MSS.[5] MSS and IFS differ considerably in treatment and prognosis, necessitating differentiation from each other.

We describe a case of a recurrent mass in the popliteal region in a 3-year-old girl. X-ray showed a heterogeneous soft tissue mass in the popliteal region with focal calcifications, with no changes in the underlying long bone or periosteum. At 6 months of age, she underwent surgery for a tumor in the same location. The relevant clinical and histological details were lost by the parents. In view of recurrence, a clinical diagnosis of IFS was made and she underwent complete excision of the tumor.

 Pathological Findings

The excised tumor measured 5 × 4 × 4 cm with muscular attachments and was grey-white on sectioning. Histopathological sections showed short sweeping bundles of monomorphic spindle cells, with three mitotic figures per 10 high-power fields, and a few myxoid areas without inflammatory cell infiltration or extramedullary hematopoiesis. Differential diagnoses of recurrent IFS and MPNST were considered.

Immunohistochemistry (IHC) showed strong and diffuse positivity for CD99 and Bcl2, strong nuclear expression of TLE1, positive EMA, and focally positive CK expression. IHC was negative for CD34, S100, myogenin, and desmin [Figure 1]. Based on these, diagnosis of MSS was made.{Figure 1}

The child received cyclophosphamide and actinomycin-D as part of postoperative chemotherapy. She is doing well on a follow-up of 2 years.

SS is the second most common sarcoma in children, after rhabdomyosarcoma.[1] Histologically, MSS shares similarities with other soft tissue sarcomas such as MPNST and IFS. MSS needs to be differentiated from IFS as they differ in their treatment protocols and prognosis. SS requires complete excision followed by radiotherapy and chemotherapy. Surgery alone suffices in case of IFS. SS can metastasize to the lungs and bones, and 5-year survival rate in children is 83%.[6] It often recurs around the knee joint and at the back. On the other hand, IFS rarely metastasizes, and 5-year survival rate is almost 100%. Recurrence rate for IFS is 5%–50%.

SS is a slow-growing painless mass most prevalent in adolescents and young adults. But cases have been reported in infants, neonates, and even preterm neonates.[2],[3],[4] It has a predilection for the lower limbs, usually occurring around the knee joint. Grossly, it is well-circumscribed, pseudo-encapsulated, and cut section is soft and grey-white. Fibrosarcoma, on the other hand, is a rapidly growing mass found in the superficial and deep soft tissues of distal extremities, less commonly in the trunk and head and neck. Fibrosarcoma is divided into two groups, the adult and the infantile types. The infantile type develops within the first 2 years of life and is often congenital. Osseous erosion may be present. Grossly, it is poorly circumscribed, lobulated, and infiltrates soft tissues. The cut surface is fleshy and tan.

Although there is histological overlap between SS and IFS, the former has certain distinct features. SS can be monophasic or biphasic. Biphasic variant has both epithelial and spindle cell components. MSS has more ovoid-appearing cells with bland but hyperchromatic nuclei arranged in sheets or fascicles. There may be foci of cells with eosinophilic cytoplasm, ropy collagen, and mast cells. There may be evidence of calcification and ossification. Mitotic activity is variable. On the other hand, IFS is composed of oval to spindle-shaped cells arranged in sheets or herringbone fascicles. Cells are monomorphic with bland nuclei. Mitotic activity is brisk. Myxoid foci can be present. Chronic inflammatory cell infiltration consisting of lymphocytes and plasma cells as well as extramedullary hematopoiesis may exist. Other histological variations include hyalinization, collagenization, fibrin thrombi, hemorrhage, necrosis, calcification, or hemangiopericytoma-like vascular pattern.

IHC and genetic studies are necessary to definitively differentiate MSS from IFS. In case of SS, TLE1 is a highly sensitive marker.[7] In a study by Rekhi et al., the overall sensitivity of TLE1 in diagnosis of SS was 95.2%.[8] SS also shows strong and diffuse positivity for Bcl 2. Cytokeratin and EMA are also positive, sometimes with patchy expression. The tumor shows focal positivity for CD99, S100, CD56, and calponin. CD34 is negative. IFS shows positivity for SMA and desmin. There is occasional expression of CD34, CK, and S100. It is negative for TLE1.

[Table 1] lists the important clinicopathological differences between SS and IFS. The detection of t(X: 18)(p11;q11) and SSX and SS18 (SYT) gene fusion is highly sensitive and specific for identifying SS.[9],[10] TLE1 has emerged as a good substitute for t(X: 18) and can be used as a surrogate marker to differentiate SS from other histological mimics in the setting of limited molecular facilities. IFS shows t(12:15)(p13;q25) and ETV6-NTRK3 gene fusion (also shared by cellular congenital mesoblastic nephroma).{Table 1}

In conclusion, SS is an important differential diagnosis of sarcomas in infants and young children, overlapping morphologically with IFS, which is more common in infants and has better prognosis and different treatment protocol. Histopathology combined with IHC and genetic studies are important to distinguish between these two entities.

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