Purpose An awareness of the distinctive morphologic and immunohistochemical features of various spindle cell tumours is essential in optimising prognostic information. Here we report a case of spindle cell neoplasm within the hypothenar eminence with unusual fusion gene SETD1B-FOSB which has never been reported before in a spindle cell neoplasm. Methodology This case report is of a 65 year old man who presented with a distinct oval mass within the subcutaneous tissue overlying the volar aspect of the hypothenar eminence measuring 24mm x 17mm x 31mm on MRI. The patient underwent an excisional biopsy and histopathological analysis. Results Histological features were those of a spindle cell neoplasm with a fibroblastic phenotype in which the morphology was unusual and the differential diagnosis broad. Additional RNA sequencing assay revealed the presence of an unusual fusion gene SETD1B-FOSB which has only been documented in intravascular haemangiomas and not yet in a spindle cell neoplasm. Although the lesion was likely benign in nature, its biological behaviour was unknown. Recommendation from the multidisciplinary soft tissue tumour meeting was for regular post-operative imaging for close tumour surveillance. Conclusion Spindle cell neoplasms arising within tissues comprise a heterogenous group of tumours with divergent lineages which can present diagnostic challenges. Important diagnostic issues include distinguishing between benign spindle cell lesions and malignancies and classifying histologic types and subtypes. This case in particular highlights how a careful histopathological diagnosis is essential for optimising patient management for this rare type of spindle cell neoplasm.