Here is our understanding of how the "unproven" status can arise for a suspicious region. Imagine that the physician sees two suspicious regions in the mammogram, but with one markedly more suspicious than the other. The physician may have a biopsy performed on only the more suspicious regions.
If the biopsy result is malignant, then the course of action is to remove the breast tissue for both regions. If the biopsy result is not malignant, then the originally less-suspicious region is considered even less suspicious.
In this way, an image which contains a path-proven cancer may sometimes also include a suspicious regions whose status remains unproven.