Cytologic Diagnoses of Lung Adenocarcinoma With Concomitant Metastasis From a Different Primary: A Case Series.

Lung adenocarcinoma is a common malignancy that can metastasize. The lung is also a common site for metastasis from other sites. Prompt and accurate diagnosis is critical for patient management. The diagnosis of lung adenocarcinoma can be occasionally challenging due to overlapping clinical and pathological features with adenocarcinomas from other origins. We present three cases of lung adenocarcinomas with concomitant metastatic adenocarcinomas of different primaries in the same endobronchial ultrasound-guided fine-needle aspiration (EBUS-FNA) or core biopsy procedures. The first case showed metastatic ROS-rearranged lung adenocarcinoma and metastatic ampullary adenocarcinoma involving different mediastinal lymph nodes, respectively, in a patient with no previous history of malignancy. The second case showed metastatic lung adenocarcinoma with MET exon 14 deletion and metastatic breast adenocarcinoma involving different mediastinal lymph nodes, respectively, in a patient with a previous history of breast carcinoma. The third case showed metastatic prostatic adenocarcinoma to a pre-existing lung mucinous adenocarcinoma in a patient with a previous history of prostatic adenocarcinoma. Our report highlights attention to details, judicious use of immunostains, and ancillary molecular studies in complex pathology cases. Cytohistological findings are also correlated with molecular test results.