Clinicopathological study of a rare GAB1::ABL1 fusion-positive spindle cell tumour: A postoperative recurrent case combined with analysis of 15 global literature cases

GAB1::ABL1 fusion-positive spindle cell tumour is a rare recently delineated neoplasm lacking an established consensus on its clinical and pathological features, treatment strategies, and prognosis. This study retrospectively analyzed the clinical diagnostic and therapeutic data of a patient with a paravertebral soft tissue GAB1::ABL1 fusion-positive spindle cell tumour of the back and compared these data with those of 15 previously reported cases retrieved from Web of Science and PubMed. The pooled analysis revealed that the tumour predominantly affects children and young adults (median age, 24 years), with the shoulder/back region being the most common site and local bony invasion observed in two cases. Fourteen patients underwent surgical resection, while two patients did not (among whom one received imatinib therapy following core needle biopsy). Follow-up data showed tumour recurrence in two cases after surgery and tumour shrinkage in one case following imatinib treatment. Histopathologically, the tumour was characterized by a predominance of morphologically bland spindle cells arranged in fascicular or storiform patterns. Immunohistochemically, the tumour cells exhibited variable expression of perineural cell-associated markers, including CD34, epithelial membrane antigen, Claudin-1, and glucose transporter 1. All patients harbored an in-frame GAB1 (exon 6):ABL1 (exon 2) fusion gene. The chimeric protein encoded by this fusion gene contains the pleckstrin homology domain of GAB1 and the complete kinase domain of ABL1, which induces constitutive activation of tyrosine kinase and subsequently activates multiple downstream pro-tumorigenic signaling pathways. In conclusion, GAB1::ABL1 fusion-positive spindle cell tumors generally exhibit an indolent biological behavior; however, their locally infiltrative growth patterns increase the risk of postoperative recurrence. The characteristic GAB1::ABL1 fusion gene serves as the core molecular diagnostic hallmark and suggests potential responsiveness to tyrosine kinase inhibitors such as imatinib. In clinical pathological practice, comprehensive ribonucleic acid fusion gene testing should be performed to confirm the diagnosis of such tumors, thereby providing molecular pathological evidence for precise diagnosis and treatment.