Cyclophosphamide and Etoposide as a Metronomic Therapy in Advanced Head and Neck Squamous Cell Cancer

The goal of this clinical trial is to learn if drugs as cyclophosphamide (C) and etoposide (E) work to treat advanced head and neck cancer in adults. It will also learn about the safety of both drugs. The main questions it aims to answer are: Do drugs C and E work to treat advanced head and neck cancer, after failure on first line chemotherapy? What medical problems do participants have when taking drugs C and E? Researchers will compare drugs C and E in combination to a placebo (a look-alike substance that contains no drug) to see if these 2 drugs works to treat advanced head and neck cancer. Participants will: Take drug C every 3 weeks and drug E every 4 weeks or a placebo every week for 6 months. Visit the clinic once every 3 weeks for checkups and tests. Keep a diary of their symptoms.