Lung mets these days are resected, or treated with radio frequency ablation and chemo therapy. The naming of all this is secondary to dealing with it. A lung cancer as a second primary is serious. A metastasis of an existing head and neck cancer to the lungs (producing the same number and size of lesions) is a real problem, this is EXPANSION of disease, not a new entity. Spread and further invasion of cancer is a difficult turn around though not impossible in comparison to a new localized cancer. Lob resection is common, and you can live with out large parts of your lungs or even just one. But the issue is why they appeared, and if they came once, they can come again... this is exacerbated by field carcinogenisis such as from tobacco smoking.

A second primary does snot have to have the same causative etiology. Again this may be from large area contamination via tobacco, or a genetic predisposition to cancers in general.