Myxoid mesenchymal neoplasm presenting as massive arm and chest wall oedema with pleural effusion.

Myxoid mesenchymal tumours are a heterogeneous group of neoplasms characterised histologically by their abundant mucoid and myxoid extracellular matrix (ECM). Encompassing a broad spectrum of clinical behaviour ranging from benign to malignant, there are more than 60 reactive and neoplastic entities currently classified under its domain. Its varied clinical and histopathologic features continue to pose a diagnostic challenge to clinicians and pathologists. Here, we describe a rare case of myxoid mesenchymal tumour presenting as oedema of the upper extremity with pleural metastasis and partial response to chemotherapy, which to the best of our knowledge has not yet been described in the literature.