 Malignant mesothelioma is an aggressive, asbestos-related tumour of the pleural and peritoneal cavities. It is a rare cancer which occurs in individuals who have been exposed to asbestos, although it typically occurs decades after exposure 10-40 years later. Malignant pleural mesothelioma forms plaques that are distributed on the surface of the pleural space in the lung. Approximately 30 of patients require an indwelling pleural catheter for drainage of pleural effusions. In this patient group, the indwelling catheter may be used to facilitate loco-regional delivery of HSV1716 to the pleural space. 