A coin lesion on chest x-ray ( this may be a nodule if less than 3cm or in this case a mass as greater than 3cm) requires further assessment.

The differential wide, although the commonest and most important to diagnosis is a bronchial carcinoma.

In the first instance review of previous imaging is indicated.  If the lesion was not previously identified then urgent referral to a respiratory physcian is indicated, during this process CT with be performed.