My mom was diagnosed with breastcancer a year ago. lump 1, 5 cm. no symptoms, pain at all! how long could she have gone with no symptoms?

Impossible to say.: Impossible to say. It depends not only on tumor size but the specific makeup of the tumor.

Quite awhile: Breast cancer often does not get painful until it gets rather large. A breast cancer usually has to be present for 5 years before it even gets big enough to feel. Usually the cancer doesn't cause pain until it invades a nearby area. Mammograms and regular examinations are essential to find breast cancer when it can most likely be cured.