Which side effects should I call my doctor about right away?

Which side effects count as urgent depends on your specific treatment, so the most reliable way to find out is to ask your care team directly. The National Cancer Institute lists "Are there any side effects I should call you about right away?" as one of the key questions to ask before starting treatment.

This is worth writing down separately from your other questions and getting a clear, specific answer to — not a general sense, but an actual list of symptoms and a phone number or portal message to use if they happen. Different treatments carry different urgent warning signs, so an answer that applies to one type of treatment may not apply to another.

It also helps to ask who to contact outside of regular office hours, since side effects don't always follow a convenient schedule. Some cancer centers have an on-call line or after-hours service specifically for this.

Having this answer ready before you need it means you won't have to guess, in a stressful moment, whether something is serious enough to call about.