Malignant transformation of pulmonary bronchiolar adenoma into mucinous adenocarcinoma:A case report

BACKGROUND Bronchiolar adenoma(BA)and ciliated muconodular papillary tumor are rare tumors that have bilayered cell proliferation and continuous expression of p40 and CK5/6 in the basal cell layer.Diagnosis is difficult because of the limited knowledge of these tumors and their morphological similarities to malignant tumors,including invasive mucinous adenocarcinoma,especially based on the histopathology of intraoperative frozen sections.These tumors are now considered to be benign neoplasms,with malignant transformation reported in only a few cases.CASE SUMMARY A 57-year-old woman presented with a 17.0 mm×7.0 mm nodule in the lower lobe of the left lung.Hematoxylin-eosin staining and immunohistochemistry of a surgical specimen were performed.The tumor consisted of a BA area and a mucinous adenocarcinoma(MA)area.In the BA area,the tumor had a bilayered structure of luminal cells and basal cells.The basal cells were positive for CK5/6 and p40,but the MA area was negative for these biomarkers.The Ki-67 proliferation index was low(1%-2%).The patient was diagnosed with BA accompanied by MA,and had a favorable outcome.CONCLUSION The present study indicated that BA may be carcinogenic,and suggests that clinicians should be aware of its potential for malignant transformation.

Bronchiolar adenoma with unusual presentation:Two case reports

BACKGROUND The clinicopathological features,immunohistochemical characteristics,and genetic mutation profile of two unusual cases of distal bronchiolar adenoma are retrospectively analyzed and the relevant literature is reviewed.CASE SUMMARY Case 1 was a 63-year-old female patient who had a mixed ground-glass nodule,with mild cells in morphology,visible cilia,and bilayer structures in focal areas.Immunohistochemical staining for P63 and cytokeratin(CK)5/6 revealed the lack of a continuous bilayer structure in most areas,and no mutations were found in epidermal growth factor receptor,anaplastic lymphoma kinase,ROS1,Kirsten rat sarcoma,PIK3CA,BRAF,human epidermal growth factor receptor-2(HER2),RET,and neuroblastoma RAS genes.Case 2 was a 58-year-old female patient who presented with a solid nodule,in which most cells were observed to be medium sized,the nuclear chromatin was pale and homogeneous,local cells had atypia,and cilia were found locally.Immunohistochemical staining for P63 and CK5/6 showed no expression of these proteins in mild cell morphology whereas the heteromorphic cells showed a bilayer structure.The same nine genes as above were analyzed,and HER2 gene mutation was identified.CONCLUSION Some unresolved questions remain to be answered to determine whether the lesion is a benign adenoma or a part of the process of malignant transformation from benign adenoma of the bronchial epithelium.Furthermore,whether lesions with atypical bilayer structures are similar to atypical hyperplastic lesions of the breast remains to be elucidated.Moreover,clarity on whether these lesions can be called atypical bronchiolar adenoma and whether they are invasive precursor lesions is needed.Future studies should examine the diagnostic significance of HER2 gene mutation as a prognostic indicator.