What is ocult breast cancer?

Occult Ca: Detection of occult tumor cells in blood, bone marrow or lymph nodes by molecular technique that usually can not be detected by imaging or standard immunochemistry in patients with breast cancer.

It is a breast: cancer detected outside the breast(for example in an axillary lymph node), in which the presumptive primary cancer within the breast cannot be detected by standard clinical and imaging methods. Not very common, accounts for less than 1% of breast cancers.