A 40-year-old woman presents to your office with constipation and vague lower back pain. On digital rectal examination, you palpate a smooth mass posteriorly at the tip of your finger. Colonoscopy findings were normal, save for posterior bulging with smooth mucosa in the rectum. Magnetic resonance imaging (MRI) shows a solid mass in the rectorectal space with bony destruction of the sacrum. What is the next best management step for this patient?