Background Nodular fasciitis is a benign and typically self-limited clonal neoplastic process. The clinical and histologic features of a rapidly growing solitary mass with high cellularity, cytologic atypia, and increased mitotic rate mean it poses a diagnostic challenge with the concerning differential being sarcoma. This stark watershed between benign and malignant means there is a risk of inappropriate overtreatment. The recent use of FISH cytogenetics helps distinguish nodular fasciitis from malignant differentials. We present a case where a history of previous testicular carcinoma added to the clinical concern for malignancy.
Case Report This 34-year-old man previously had a mixed germ cell tumour comprising immature teratoma, seminoma and embryonal carcinoma components. He underwent an orchidectomy and, after recurrence, chemotherapy which was completed 10 years prior. He presented with a firm mobile mass on the right forearm present for around two months. Ultrasound showed a solid mass with internal vascularity measuring 18 x 17 x 6 mm. The lesion was excised and found to be adherent to fascia with a plane between this and underlying muscle. Histology revealed a relatively well circumscribed highly cellular spindle cell lesion with a brisk mitotic rate and minor cytologic atypia. Ubiquitin specific protease 6 (USP6) gene rearrangement was able to identify this lesion as nodular fasciitis and therefore benign.
Discussion There have been rare case descriptions of soft tissue metastases of testicular carcinoma and reports of an increased risk of soft tissue sarcomas in patients who have undergone chemotherapy for testicular cancer. Any new soft tissue mass in this setting raises concern for malignancy. USP6 has emerged as a useful diagnostic adjunct for identifying nodular fasciitis
Conclusion In this case, histology has shown a benign process but serves as a reminder of nodular fasciitis as a pseudosarcomatous mimic.