Does breast cancer show up in blood tests?

Yes: Yes it does, but you have to specifically order the correct tumor marker and not all breast cancers have elevated blood levels of tumor markers. This means that it is not a good way to monitor for breast cancer.

Not really.: Apart from tests for genetic markers, breast cancer is usually diagnosed from self exam or mammography where a mass is detected. If it persists throughout the cycle, or is in postmenopausal women, it should be aspirated. If the fluid is bloody or leaves a residual mass, or the original mass is solid, a mammogram and excisional biopsy are done.