Biphasic synovial sarcoma with a striking morphological divergence from the main mass to lymph node metastasis: A case report

Abstract

Rationale: Synovial sarcoma accounts for 5% to 10% of all soft tissue sarcomas and involves almost any anatomic site, particularly the deep soft tissue of the extremities of young adults. The incidence rate of lymph node metastases in synovial sarcoma is 3% to 7%, but the detailed morphological features of the metastatic tumors in the lymph node have not been documented.

Patient concerns: A 64-year-old Korean man presented with a huge mass in the left lower thorax and multiple hypermetabolic lymph nodes along the mediastinal, supraclavicular, internal mammary, and retrocrural regions.

Diagnoses: The patient was diagnosed with primary pleuropulmonary biphasic synovial sarcoma with lymph node metastases, where the main mass mostly comprised spindle cells (>95%) and the metastatic lymph nodes comprised only epithelial cells.

Interventions: Left lower lobe lobectomy with the resection of the chest wall (including left ribs 8-10) and diaphragm and mediastinal lymph node dissection were performed.

Outcomes: In the 2-month follow-up period, there have been no complications so far, and the attending physician is currently planning for the adjuvant chemotherapy.

Lessons: The main mass and the metastatic lesion can be clearly different morphologically. In tumors with biphasic differentiation, such as synovial sarcoma, cells that constitute only a small fraction of the main mass may appear as the dominant cells in metastatic lesions.

Figure 1

(A) Coronal computed tomography image demonstrates a well-defined mass with internal necrosis in the left lower hemithorax. (B) Gross specimen shows a well-defined solid mass, which contains geographic necrosis and hemorrhage and involves the lung (the left side of the photo), ribs (the bottom of the photo), and diaphragm (the right side of the photo).

Figure 2

The representative images of the main mass (A-F) and the metastatic lymph node (G-L). The main mass predominantly (>95%) comprised dense cellular sheets and fascicles of uniform spindle cells (A) with ovoid vesicular nuclei, inconspicuous nucleoli, and sparse eosinophilic cytoplasm (B). At the periphery of the tumor, a small fraction (<5%) of the tumor exhibited epithelial differentiation, forming varying-sized cords (C) and solid nests (D). The tumor cells were diffusely and strongly immunostained with transducin-like enhancer of split 1(TLE1) (E) and focally and weakly with pan-cytokeratin (F). The metastatic lymph nodes showed purely epithelial component in micropapillary architecture (G and H, frozen section) and solid nests (I and J). The tumor cells were diffusely and strongly immunostained with TLE1 (K) and pan-cytokeratin (L). (Original magnification: [A] ×200, [B and C] ×400, [D] ×200; [E-F] ×400, [G] ×100, [H] ×200, [I] ×100, [J] ×200, [K and L] ×400).

Figure 3

The result of real-time polymerase chain reaction for SS18 (SYT)-SSX translocation confirms the presence of the translocation in our case (yellow arrow).