It can be very difficult for even doctors to tell the difference between headaches (or full-on migraines) caused by brain tumors and those resulting from other reasons. 'The best indicator is a new daily headache that won’t seem to go away,' says Mike Chen, MD, PhD, associate professor, division of neurosurgery, department of surgery at City of Hope. 'These headaches tend to get worse over time and are often present when you wake up in the morning, when intracranial pressure is high from lying in bed for hour-long periods of time.' (Here's how to naturally treat your headaches). This pain can vary greatly regardless of the size or growth rate of the tumor. 'A small, fast-growing tumor can cause as severe of a headache as a large, slow-growing tumor,' says Santosh Kesari, MD, PhD, neuro-oncologist and chair of the department of translational neuro-oncology and neurotherapeutics at John Wayne Cancer Institute in Santa Monica, California. And there’s no specific type of headache that can predict whether or not a person has a brain tumor. The key is to be on the lookout for new, persistent headaches that do not respond to any treatments, such as over-the-counter medicines. Here are subtle signs of cancer women are likely to ignore.