BACKGROUND: Primary pulmonary myxoid sarcoma (PPMS) is a rare, low-grade malignant tumor, constituting approximately 0.2% of all lung tumors. Despite its rarity, PPMS possesses distinctive histological features and molecular alterations, notably the presence of EWSR1-CREB1 gene fusion. However, its precise tissue origin remains elusive, posing challenges in clinical diagnosis.
UNASSIGNED: A 20-year-old male patient underwent a routine physical examination 6 months prior, revealing a pulmonary mass. Following surgical excision, microscopic evaluation unveiled predominantly short spindle-shaped tumor cells organized in a fascicular, beam-like, or reticular pattern. The stromal matrix exhibited abundant mucin, accompanied by lymphocytic and plasma cell infiltration, with Russell bodies evident in focal areas. Immunophenotypic profiling revealed positive expression of vimentin and epithelial membrane antigen in tumor cells, whereas smooth muscle actin and S-100, among others, were negative. Ki-67 proliferation index was approximately 5%. Subsequent second-generation sequencing identified the characteristic EWSR1-CREB1 gene fusion. The definitive pathological diagnosis established PPMS. The patient underwent no adjuvant chemotherapy or radiotherapy and remained recurrence-free during a 30-month follow-up period.
CONCLUSIONS: We report a rare case of PPMS located within the left lung lobe interlobar fissure, featuring Russell body formation within the tumor stroma, a novel finding in PPMS. Furthermore, the histomorphological characteristics of this case highlight the diagnostic challenge it poses, as it may mimic inflammatory myofibroblastic tumor, extraskeletal myxoid chondrosarcoma, or hemangiopericytoma-like fibrous histiocytoma. Therefore, accurate diagnosis necessitates an integrated approach involving morphological, immunohistochemical, and molecular analyses.

Primary pulmonary myxoid sarcoma (PPMS) is an extremely rare malignant mesenchymal tumor of the lung, with only less than 40 cases reported. We described a case of a 64-years-old man with a mass on the medial and lower lobe of the right lung confirmed as a primary pulmonary myxoid sarcoma on biopsy. Diagnosis of this tumor remains challenging because of its nonspecific clinical and imaging characteristics. This study emphasizes CT finding to improve the understanding of PPMS.

BACKGROUND: Primary pulmonary sarcoma is extremely rare and mostly metastatic, and primary pulmonary myxoid sarcoma PPMS is a rare low-grade malignant sarcoma. The clinical manifestations of PPMS patients are relatively non-specific, sometimes found by physical examination. We report a case designed to explore the clinicopathologic features, diagnosis, and differential diagnosis of primary pulmonary myxoid sarcoma (PPMS). A 44-year-old man was found to have a primary myxoid sarcoma in the upper right lung on physical examination. The patient did not have any symptoms of discomfort. Histologically, the tumors had well-defined borders, and with grayish-white or grayish red cut surfaces. Under the microscope, the tumor cells were composed of oval and spindle cells arranged in a network or strips in a mucus-like stroma. Immunohistochemically, neoplastic cells showed diffuse and strong vimentin expression and focal weak EMA, and Bcl-6 staining. The expression of AE1/AE3, ALK, CD34, CD68, SMA, and CD99 were all negative. The Ki-67 index was low.
CONCLUSIONS: PPMS is a rare low-grade malignant primary pulmonary sarcoma without characteristic clinical symptoms and difficult to diagnose. It is mainly diagnosed by immunohistochemistry and genetic testing.

Primary pulmonary mesenchymal tumors are rare, yet they compromise a variety of entities. A novel low-grade malignant neoplasm coined primary pulmonary myxoid sarcoma (PPMS) has been introduced in the WHO classification of lung tumors. Molecular analysis in PPMS revealed recurrent gene fusions between EWSR1 and CREB1, a member of the cAMP response element binding protein (CREB) family. However, only 23 PPMS have been reported in the literature reflecting their exceedingly low incidence. Here, we describe the case of a 41-year-old female patient with a lung tumor obstructing the right main bronchus. Histologically, the tumor was composed of spindle-shaped and epithelioid cells exhibiting a reticular growth pattern within a prominent myxoid matrix. Solid areas were also observed. Molecular analysis by next-generation sequencing identified a fusion transcript with an unusual gene fusion involving exon 7 of EWSR1 and exon 5 of CREB1. Together, the diagnosis PPMS was established.

Primary pulmonary myxoid sarcoma (PPMS) is a recently defined rare neoplasm with histological and molecular similarity to extraskeletal myxoid chondrosarcoma. To date, 20 cases have been reported. A 48-year-old man presented with a huge mass filling the right hemithorax and extending into the tracheobronchial system. Histological findings were consistent with PPMS. Immunohistochemistry was positive for vimentin, CD10, and EMA, but other lineage-specific markers were negative. SMARCB1 (INI1) expression was lost in the tumour cells. FISH analysis (EWSR1, FUS, NR4A3, and SMARCB1) revealed no abnormalities. This case suggests SMARCB1 loss as a possible alternative molecular event driving EWSR1-negative PPMS.