A 40-year-old female patient presented to the outpatient department of tumor hospital of Hebei Province with a groin mass present for more than 2 mos, alongside pain for 1 wk. Physical examination revealed swelling of the groin, with purplish skin on the surface, and no ulceration. Ultrasonography showed a subcutaneous mixed echo occupying space, approximately 6 × 6 × 3 cm in size, with a regular shape, and a clear boundary. The patient had no other symptoms or signs; therefore, she was admitted to the hospital for surgical treatment.
After the operation, gross pathological examination showed a nodular mass measuring 6 × 5.5 × 2 cm, with a solid mass, a grey and white section, tough, clear boundary, and no obvious capsule. Subsequent microscopic observation then showed that the morphological features were composed of cell bundles with spindle nuclei and interwoven fine collagen fibres. The tumour nuclei were uniformly stained, with abundant cytoplasm, large nucleoli, easily visible mitosis, and arranged in vortex- or wheel-like structures. The surrounding tumour infiltrated the surrounding adipose tissue. Immunophenotyping showed that VIM and CD34 were strongly diffusely positive, while CD68, CD163, and SMA were focally positive, and S100 and STAT6 were negative. These immunohistochemical expression patterns helped rule out a diagnosis of dermatofibrosarcoma protuberans (DFSP). However, when we performed immunohistochemical staining for the novel markers pan-TRK and BRG1, we found that both were negative. Pan-TRK is a marker related to targeted therapy, and negative immunohistochemistry results indicate that the corresponding targeted drug cannot be used(Fig. 1). However, a negative BRG1 result indicates a loss of the SMARCA4 gene, which is rare.
To further verify the presence of the SMARCA4 gene deletion, RT-PCR and next-generation sequencing(sequencing depth 1000×, ) were performed, and the results subsequently confirmed the presence of SMARCA4 gene deletion in this case of DFSP(Fig. 2). Such cases have not been previously reported. After a complete tumour resection, the tumour stage was determined as T2N0M0. No subsequent treatments were required. At the follow-up after 1 year, no recurrence or metastasis was observed.