Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for a prolonged seizure, loss of consciousness, severe breathing difficulty, or sudden stroke-like symptoms.
Seek urgent medical advice for rapidly worsening headache, repeated vomiting, increasing sleepiness, new weakness, new speech or vision problems, or a major change in behavior or thinking.
Follow-up usually includes neurological examinations and repeat MRI scans.
Timing depends on the tumor type, grade, molecular findings, treatment, symptoms, and time since diagnosis.
Scans are often more frequent soon after treatment.
Follow-up should also address seizures, medication side effects, rehabilitation, mood, sleep, memory, hormone function, work, and driving.
Report new or worsening symptoms rather than waiting for the next appointment.
The article also says
MRI changes after radiation or chemotherapy do not always mean that the tumor is growing.
Inflammation or tissue injury can resemble progression, so specialists may compare several scans, use advanced imaging, or occasionally recommend another biopsy.
Every sign above is quoted from the sofidex article on Brain tumor - primary - adults. If you are not sure, err upward — it is always reasonable to be checked.