A clinicopathological study of eight cases presenting a Biphasic structure: A distinct variant of pulmonary carcinoma

Biphasic structures, which are composed of outer basal cells and inner glandular cells, are frequently indicative of salivary gland-type tumors or benign lesions, such as bronchial adenoma, within the lung. However, the occurrence of a biphasic structure in lung cancer is rarely reported and can lead to significant challenges and confusion in diagnosis, particularly in biopsy specimens. In our study, we collected eight lung epithelial tumors that presented with a distinct biphasic structure component and examined their clinicopathological characteristics. Histological examination revealed that the biphasic structure component, often intermingled with conventional squamous cell carcinoma or adenocarcinoma, was defined by basal cells encircling the glandular epithelium. Immunohistochemical analysis demonstrated a distinctive peripheral p40 staining pattern in the biphasic structure component. Genetic analysis identified driver mutations in seven out of eight patients, which are typically associated with conventional pulmonary adenocarcinomas, including EGFR L858R, EGFR 19-del, EGFR 20-ins, and KRAS mutations. The presence of biphasic structure components in these cases confirms a genuine form of lung cancer, likely representing a variant of lung adenocarcinoma. This study's findings enhance the understanding of lung cancer's morphological diversity and caution against prematurely dismissing the malignancy potential of pulmonary epithelial lesions based solely on the presence of basal cells, especially with biopsy specimens.