A Multi-omics Approach to Disclose Progression and Underlying Biology of Head and Neck Adenoid Cystic Carcinoma

The goal of this observational study is to better understand why some people with metastatic adenoid cystic carcinoma (ACC) of the head and neck have slow-growing disease while others have faster-growing or more aggressive disease. Researchers want to learn how the biology of the tumor relates to each person's clinical risk group, which is based on a published prediction tool (a nomogram). The main question the study aims to answer is: Do people in the high-risk and low-risk groups have different biological tumor types (called ACC-I and ACC-II) when their primary tumor is tested? The study will also look at other important questions, such as: * Do metastatic tumors show the same biological type as the original tumor? * Do biological types differ based on where metastases grow or how early or late they appear? * Are biological types linked to how well systemic treatments work? * Can blood tests (including DNA fragments or small RNA molecules in the blood) show the same tumor biology and help track how the cancer changes over time? Participants will: * Allow researchers to study samples of tumor tissue taken in the past during standard care. * Give blood samples at study entry and then every 6 months for up to 2 years. * Continue all medical treatments and follow-up visits as decided by their own care team. * Receive no study treatment; this study only collects information and samples. About 114 adults with metastatic ACC of the head and neck will join the study. People with only local or regional recurrence (without metastases) or those whose primary tumor started outside the head and neck cannot take part. The information gathered may help researchers understand why ACC behaves differently from person to person, identify new biological markers in blood, and support future personalized treatment strategies for people with metastatic ACC.