Why is this finding suspicious for malignancy (versus more benign skeletal lesion e.g. fibrous dysplasia)?
The extent of associated soft tissue mass is unusual for non-neoplastic lesions. Langerhans cell histiocytosis could theoretically appear similar.
Why is this finding unlikely a metastasis?
The patient is older than a typical age range for neuroblastoma, which is the most likely malignancy to present with such a metastatic lesion. Other tumors that involve the chest wall (e.g. breast, lung carcinoma) are mostly in adults.
Mixed lytic/sclerotic lesion involving the right lateral 10th rib with associated soft tissue density surrounding the lesion.
Given patient's age, finding is most suspicious for a primary neoplasm, unlikely metastasis. Recommend CT for further evaluation.