Patient presents with suspected lung metastasis, secondary malignancy, or metastatic lung disease.  Presenting symptoms include persistent cough, hemoptysis, dyspnea, chest pain, pleural effusion, and fatigue.  On physical examination, findings may include decreased breath sounds, dullness to percussion, or wheezing.  Imaging studies, such as chest X-ray, CT scan of the chest with contrast, or PET scan, reveal pulmonary nodules or masses suggestive of metastatic disease.  Diagnostic workup may include biopsy of the lung lesion for histopathological confirmation and immunohistochemistry, bronchoscopy, and thoracentesis if pleural effusion is present.  Differential diagnosis includes primary lung cancer, benign pulmonary nodules, granulomas, and infections.  The primary cancer site is being investigated.  Patient history includes colon cancer, breast cancer, or melanoma.  The stage of lung metastasis is determined based on the extent of spread.  Treatment options for lung metastasis include chemotherapy, targeted therapy, immunotherapy, radiation therapy, palliative care, and supportive care.  Patient education regarding prognosis, treatment side effects, and follow-up care is provided.  Medical coding may involve ICD-10 codes for secondary malignant neoplasm of lung (C78.0), specific primary malignancy sites, and relevant procedures.  Billing codes will reflect the diagnostic and therapeutic interventions performed.  Ongoing monitoring of disease progression and treatment response will be conducted through serial imaging and clinical evaluation.  Referral to oncology, pulmonology, and palliative care specialists as needed.