Use of a highly sensitive lung cancer compact panel to detect KRAS G12D in the wash fluid from a lung tumor: A case report

Here, we report a case of a pulmonary invasive mucinous adenocarcinoma harboring KRAS G12D, diagnosed from tumor samples containing a very small amount of tumor cells using next‐generation sequencing (NGS) and the recently developed Lung Cancer Compact Panel. A 79‐year‐old woman without any respiratory symptoms underwent chest computed tomography, which revealed a tumor in the left lower lobe. During endobronchial ultrasound (EBUS)‐guided transbronchial biopsy (TBB) using a guide sheath (GS), a sufficient specimen for pathological diagnosis could not be obtained because the patient had a severe cough and pulmonary bullae located adjacent to the tumor. In the absence of EBUS transbronchial biopsy findings using a guide sheath, brush cytology was used to categorize the tumor as class II (Papanicolaou classification). However, the wash fluid from the cytological examination contained enough cells to obtain sufficient nucleic acid for use in sequencing analysis. The latter revealed KRAS G12D expression. Although the patient underwent surgery without pathological evidence, the evaluation of the surgical specimen confirmed a diagnosis of pulmonary invasive mucinous adenocarcinoma. Use of the Lung Cancer Compact Panel enabled the detection of KRAS G12D in the wash fluid of a brush cytology sample and thus a diagnosis of pulmonary invasive mucinous adenocarcinoma.