Multiple Lung Nodules and Breast Cancer

My sister is undergoing treatment for what, until now at least, had been deemed Stage 1 breast cancer.  She has triple negative breast cancer, an aggressive sub-type of the disease.  She just finished chemotherapy today, but also got the results of a chest CT scan today which showed 5 small nodules (all 4mm or less) in her lungs (right and left.)  Previous chest x-ray in December 2008 was clear, as were a combined PET/CT body scan in January.  The CT report does not state whether there are calcifications present.  I have read that most very small lung nodules are not cancerous, but is this true even for someone with cancer elsewhere? What might a radiolgost see on a CT scan which would suggest or rule out metastasis?  Thank you for your help.