Would signs of breast cancer show up on a regular chest ex ray or would that only show up on a mammogram?

No on X-ray : Mammograms are the best diagnostic test to diagnose breast cancer. Coupled with good breast exams and ultrasounds - these are the mainstays of diagnosis. Chest x rays can show advanced cancer if there is metastasis (spread) to the lungs - but typically regular x-rays are not sensitive or specific enough.

Mammogram: If breast cancer is very advanced and there are lung masses (stage IV spread by the blood stream) then it could be seen on a chest x-ray. Mammography is of course dedicated to finding breast cancer early and is the appropriate test. In a person who is not quite ill, an abnormal chest x-ray likely has another explanation.

Mammogram: Although the breast shadows do show up on a regular chest xray, cancer in the breasts cannot be diagnosed on a chest xray. Mammogram is the main diagnostic tool for breast cancer, complimented by breast ultrasound and MRI in specific situations.

Breast cancer: would not show up on a chest X-ray, unless it was metastatic to the lungs or visualized bones. Mammography is the standard for breast cancer screening, with ultrasound a common adjunct study. Breast MRI also has value in certain circumstances.