Hypoxia Induced Radio Resistance in Head and Neck Cancers

Surgical resection with postoperative adjuvant radiotherapy remains as “gold standard” in treating head and neck cancers. However, high recurrence and metastasis rates remain the main causes of tumor-related mortality. Hypoxia is known as one of the most important contributing factors affecting the cancer radiotherapy efficacy and it is significantly contributed by the irregular functions of tumor vasculature. In this article, we used Photoacoustic (PA) imaging method to detect oxyhemoglobin saturation in oral squamous cell carcinoma (OSCC), mucoepidermoid carcinoma (MEC) and adenoid cystic carcinoma (ACC) in mouse model and compared it with the recurrence rate and metastasis rate obtained at follow-up. MEC patients have the lowest recurrence rate (15.6%) and MEC tumors have relatively high oxygen levels. OSCC and ACC are more hypoxic and have high recurrence rates (37.5% and 39.5%, respectively). It can be proven that local hypoxia in tumor microenvironment markedly reduces the therapeutic efficacy of radiation therapy. However, ACC with relatively abundant tumor blood vessels has a high metastasis rate (50%) at the same time for it is usually at an advanced stage at the time of diagnosis. It warns us that stimulating blood vessel growth to relieve hypoxia is an undesirable solution. Other strategies such as hypoxia-responsive drugs are feasible to alleviate or respond to hypoxia.