Primary pulmonary synovial sarcoma: A clinicopathological study of 22 cases

Primary pulmonary synovial sarcoma (PPSS) is a rare mesenchymal tumour with characteristic translocation SS18-SSX1/2/rarely 4 fusion transcripts, and presents most often in adolescents and young adults. According to the World Health Organization (WHO) classification, synovial sarcoma is a malignant tumour of uncertain differentiation.

To present a case series of PPSS with clinical, pathological and molecular analysis at a rare primary site.

Retrospective study conducted in a tertiary care hospital.

Twenty-two cases of PPSSs were retrieved from electronic database between January 2009 to December 2018. Metastatic tumours from soft tissue primaries were excluded. Immunohistochemistry (IHC) and reverse transcription polymerase chain reaction (RT-PCR) were performed. Statistical analysis was performed using Mann-Whitney non-parametric test.

Among 22 patients, the male-female ratio was 3.4:1 and the median age was 31.5 years. The tumours were classified as monophasic (90.9%) and biphasic (9.1%) subtypes and graded as grade 2(77.3%) and grade 3(22.7%). IHC demonstrated expression of TLE1 (17/17 cases), Bcl-2 (7/8 cases), focal EMA (16/17 cases), CD99 (10/11 cases), focal pancytokeratin (8/12 cases) and CD56 (14/14 cases). The fusion transcripts included SYT-SSX1(4/11, 36.4%) and SYT-SSX2 (2/11, 18.2%). The remaining five cases were negative for SS18 rearrangement by RT-PCR. Only 8 patients had localised tumour. Surgical excision was performed in 5 patients. The median follow-up period was 6 months and 21 days.

Monophasic SS was the most common subtype. Small core biopsies pose a diagnostic challenge, in such a scenario, a combination of clinical, histomorphological, immunomarkers and genetic studies help confirm the diagnosis of PPSS.