Pulmonary Oligometastases: Histological Features and Difficulties in Determining Site of Origin

Introduction. Pulmonary oligometastases are resected both for diagnostic and therapeutic reasons. The histological features may be nonspecific, resulting in diagnostic difficulties. Design. The authors retrospectively studied the clinical and pathological features of 73 open resections of lung metastases from 64 patients to determine the frequency and types of problems in establishing site of origin. Results. There were 18 primary organ sites, the most frequent being colon (n = 10), head and neck (9 squamous and 6 salivary gland), kidney (n = 7), and soft tissue (n = 7). Unusual histological features included detached alveolar tumor clusters at the periphery (83% of adenocarcinomas), lepidic spread (2 metastatic pancreatic tumors), and entrapped pneumocyte-lined cysts (6 tumors). A majority of squamous carcinomas from the head and neck presented difficulties in regard to excluding a second primary, especially 4 with basaloid features that mimicked primary basaloid lung carcinoma. Other tumors mimicking lung primaries included pancreatic, endometrial, and breast metastases. Germ-cell tumors, sarcomas, melanomas, and sarcomatoid carcinomas presented diagnostic difficulties. Overall, comparison with the primary tumor with or without immunohistochemical studies was performed in 38 of 73 cases (52%). Conclusions. Pulmonary oligometastases comprise a wide range of histological types and often require careful pathological evaluation to determine primary site of origin.