Peripherally located occult lung cancer with AMFR expression.

A 67-year-old man was referred to our hospital because of positive sputum cytology. Despite detailed examination, the malignant cell source remained elusive. Twenty months later, CT revealed two nodules in the right S1 and S10 regions which were resected. A year following the operation, gastoendoscopy showed a stomach tumor. Total gastrectomy with lymph node dissection was performed. Histologically, this patient was diagnosed with double primary lung cancer with metastasis to the stomach. The tumors of the lung, stomach and tumor cells in the sputum showed the same immunoreactivities of autocrine motility factor receptor (AMFR). In our institution, of 38 occult lung cancers encountered during the past 10 years, four (10.5%) occurred in the peripheral region. The presented four cases of radiologically occult lung cancer in the peripheral resion revealed bad prognosis, as three out of four patients were dead within 24 months after surgery. All of the four cases showed venous invasion, though the size of the primary tumor was small. Careful follow-up, including monitoring for distant metastasis, is necessary in radiologically occult peripheral lung cancer.