Hi @shellfish, welcome to the forum.
I found this thread of people discussing a secondary diagnosis in the lung here, which you may find helpful: Secondary breast cancer mets to lungs
We also have information page about this here: Secondary (metastatic) breast cancer in the lung | Breast Cancer Now
We hope you find the forum useful - there are many people who are very happy to share stories and experiences, and if you ever with to ask questions straight to our nursing team, you can do so here: Ask our Nurses your questions - Breast Cancer Now forum
Sending our warmest wishes
Bernard