Mass A mass in the breast is a focal-defined lesion identified in two views on a mammogram, or felt during breast examination.
Some masses are due to cancer and others are due to benign conditions.
Most masses found are due to non-cancerous processes. When a radiologist identifies a mass on a mammogram, the first determination is whether the mass is new or has changed from its prior appearance. Masses that have not changed for two years are usually not due to cancer. Masses that have not changed in four years are almost never due to cancer. New masses may or may not be due to cancer.