Can breast cancer cause fainting?

It can, indirectly.: If you just received the news of having breast cancer, the anxiety and stress associated with that can make your heart skip a beat and make you faint. Also, pain medication and chemotherapy regimens that patients with breast cancer sometimes receive can make one weak and dizzy.

Very rare: Fainting should not be a sign of breast cancer unless widely metastatic or with brain metastases. Even then it would be uncommon. Check with your doc for more typical reasons for fainting.

Not usually : You may be feeling faint because of anxiety which is very common after being diagnosed with breast cancer otherwise you may need a cardiac work up.