What is the primary source of Bull's eye or Target metastases?

The primary source of Bull's eye or Target metastases is the lung, which typically manifests as round, nodular lesions with a specific appearance on imaging. This pattern occurs due to the unique characteristics of the lung and its blood supply, which allow for the infiltration of certain tumors, particularly those arising from malignancies such as breast, colorectal, and renal cancers. The metastatic lesions often present with a central region of necrosis surrounded by a thin rim of viable tumor, creating the characteristic target appearance.

The lung is particularly significant because it acts as a filter for venous blood returning to the heart, and any cancerous cells that enter systemic circulation can easily lodge in the lung tissue. This makes the lung a common site for metastases, leading to the Bull's eye pattern seen on imaging studies.