There are many findings to observe in this case.
1. Of most immediate importance is the large left paramediastinal mass. Associated thickened reticular markings in the left midzone suggest associated lymphangitis carcinomatosis. Note the surgical clip over the left hemithorax; there has been prior surgery and this is either a recurrent or metachronous malignancy. The lungs are hyperexpanded, indicating COPD as the background risk factor.
2. The patient has had prior breast cancer. Bilateral breast implants are present, of which the right is calcified, and there is a surgical clip in the right axilla, which points to a prior axillary dissection.
3. There is situs inversus. Note the dextrocardia, right sided aortic arch and the gastric bubble located below the right hemidiaphragm.
If not appreciated, the latter finding might confuse localisation of the lung mass. The aortic border is well visualised on the left. It is important to realise that this represents the ascending aorta located anteriorly, and not the descending aorta. The mass is therefore likely posterior/prevertebral - and this is confirmed on the subsequent CT.