Because of cancer of his larynx, mr. orwell underwent a/an, which is the surgical removal of the larynx.

I believe that Mr. Orwell underwent Laryngectomy. Laryngectomy is the partial or complete surgical removal of the larynx, usually as a treatment for cancer of the larynx. Because of its location, the larynx plays a critical role in normal breathing, swallowing, and speaking. The procedure is normally performed to remove tumors or cancerous tissue.