Arm malignant peripheral nerve sheath tumour: a rare clinical presentation.

Soft tissue sarcomas account for about 1% of malignant tumours. More than 50 subtypes of these tumours have been described with some being extremely rare, namely malignant peripheral nerve sheath tumours (MPNST). The authors present a case of a man aged 81 years with a medical history of an adenocarcinoma of the rectum, which was referred to our clinic due to a growing painless mass on the right arm. An MRI showed a well-delimited encapsulated mass involving the long head of the biceps muscle. Biopsy findings revealed a spindle cell tumour with cytonuclear pleomorphism. The patient underwent wide tumour excision and was successfully reconstructed with a latissimus dorsi functional muscle transfer. The presence of two pulmonary nodules on CT scan staging implied a lung biopsy that showed rectum primary tumour metastases. With these additional findings, the pathology department reassessed the case and reclassified the arm tumour as an MPNST, synchronous with pulmonary adenocarcinoma metastases of the rectum.