Recurring headaches that persist over time. This is one of the most insidious symptoms of a brain tumor, as even an experienced physician may have considerable difficulty in differentiating between a headache that is a symptom of a tumor, and one that has a more mundane source. It has been observed that headaches that are caused by tumors are exceedingly persistent on a daily basis, and will be all but impossible to be rid of. They will also become more intense as time passes, often manifesting in the early morning when the supine posture of sleep increases pressure in the cranium. Note that the intensity of the pain is no indication of the respective size or malignancy of the tumor.