Molecular Analysis of Liquid Cytological Samples Collected by Bronchoscopy with Radial Endobronchial Ultrasonography and Guide Sheath

: A 64-year-old man who underwent sigmoid resection for Stage 4 colon cancer had a growing nodule on the left upper lobe during follow-up. Surgical resection revealed primary pulmonary adenocarcinoma. Subsequently, a new nodule appeared in the contralateral S(1)b, for which endobronchial ultrasonography with a guide sheath (EBUS-GS) was performed for diagnosis. However, histopathologic examinations were inconclusive. Gene analysis of the liquid samples from this lesion revealed KRAS mutation, which on hindsight was not detected in the metachronous left upper lobe cancer but was detected in the resected sigmoid colon. Hence, the right upper lobe nodule was diagnosed by bronchoscopy as colon cancer metastasis, confirmed after wedge resection. For specimen obtained by EBUS-GS, search for gene mutation in the liquid specimen is useful as an ancillary test especially when histological diagnosis is equivocal. Thus, developments on diagnostic tools using liquid samples are highly expected in the future.