Matching Primary Tumor and Blood Gene Expression Analysis of HPV-negative Squamous Head and Neck Cancers

The goal of this observational study is to learn whether a blood test can show the same biological features as the tumor in people with head and neck cancer that is not caused by HPV. These cancers often have different biological types, and these types may help predict how the cancer will behave. Today, these types can only be found by studying tumor tissue. This study wants to see if a simple blood sample can give the same information. The main questions the study aims to answer are: * Can a blood test identify the same tumor type that researchers find by studying tumor tissue under a microscope and through genetic testing? * Can these blood test results help predict how people may do after finishing treatment? Researchers will not assign treatments. All participants will receive the treatments recommended by their own care team as part of routine care. Participants will: * Give a blood sample before starting treatment. * Give another blood sample about 3 months after finishing treatment. * Allow researchers to use a sample of their tumor (already collected as part of standard care) for genetic testing. * Continue routine follow-up visits with their care team. About 300 adults with locally advanced, HPV-negative head and neck cancer (affecting the mouth, throat, voice box, or hypopharynx) will take part. Only people who are receiving treatment to cure their cancer can join. People with returning cancer or cancer that has already spread cannot join. Researchers will study: * Gene activity in tumor tissue * Gene activity in blood * Patterns in blood fragments and small molecules * Digital images of tumor samples using computer-based tools The study will compare these different types of information to see whether a blood test can reliably show the tumor's biological type. If it can, this could make it easier to monitor the cancer after treatment and may help guide future care. This study does not test any new drug or treatment. It collects information that may help improve care for people with HPV-negative head and neck cancer in the future.