Cutaneous metastatic osteosarcoma – A rare case report

Introduction/Objective Osteosarcoma is an aggressive malignant primary bone tumor with common metastases to lungs via hematogenous spread. Other common sites of metastasis include bone and kidneys. Metastasis (excluding extraskeletal) to the skin is extremely rare. To date, roughly 12 cases of cutaneous metastasis have been reported in the literature. Methods/Case Report We report a 44-year-old female patient with a history of osteosarcoma of proximal tibia who underwent wide local excision in 2018 and subsequent chemotherapy. Approximately 2 years after her initial diagnosis, she presented with a painful mass in the left mid-thigh. Imaging studies revealed a 1.7 cm calcified nodule suspicious for metastatic osteosarcoma or a partially calcified granuloma. Fat necrosis and old hematoma were also considered in the radiographic differential, although less likely. An excisional biopsy was performed, which showed a high grade osteoid-producing tumor involving the deep dermis and subcutaneous adipose tissue confirming a metastasis of osteosarcoma. A new skin nodule developed at the same site six months later; though radiographic imaging studies were suggestive of subcutaneous fat stranding in the setting of cellulitis or vascular insufficiency. Given her prior history, another excisional biopsy was performed, which showed recurrent metastatic osteosarcoma. Results (if a Case Study enter NA) NA Conclusion Metastatic osteosarcoma to the skin is a rarely reported event in the literature. The prior clinical history and high index of clinical suspicion are essential in rendering the correct diagnosis. As the skin may be the first site of metastases it is important to include metastatic osteosarcoma in the differential in patients with a prior history of osteosarcoma who develops new skin or subcutaneous lesions. This case highlights the importance of providing history to the pathologist, as other tumors and non-neoplastic lesions can mimic osteosarcoma, particularly in small biopsy specimens. The easier access to the skin/ subcutis could also aid in obtaining tissue for molecular testing.