Symptoms can present as those previously outlined in section 2.1. For patients treated with surgery, signs of residual disease may also include the tumour invading vital structures that cannot be resected or pathological examination identifying extensive involved margins. For patients treated with (chemo)radiation therapy, signs of residual disease may include a clinically apparent tumour that increases in size during treatment or has not fully resolved within the timeframe expected for the specific tumour type. Diagnostic imaging evidence of residual disease on post-treatment scans may also be apparent. FDG-PET is particularly useful in assessing this.