Lung to lung metastasis is seen in -

Pulmonary metastasis from primary lung cancer and its treatment. On admission, pulmonary metastases were radiographically found in 44 of 529 patients with adenocarcinoma (8.3%), 8 of 427 patients with squamous cell carcinoma (1.9%) and 2 of 150 patients with small cell carcinoma (1.3%) Ref Harrison 20th edition pg 559