Breast densities have the following significance:
Increased basal markings could be due to breast tissue, especially from lactating breasts.
Evaluate significance of basal changes in lateral view.
Asymmetry of breast can be normal, but can also suggest a disease process.
A missing breast indicates surgical resection for breast cancer (most likely reason) and can suggest etiology for the observed lung lesion.
Hyperlucency of bases is expected when one breast is missing.