Multiple Pulmonary Papillary Adenoma With Malignant Potential Accompanied by ERBIN-BRAF Gene Fusion and APC Mutation: A Case Report and Literature Review.

backgroundPulmonary papillary adenoma is currently considered a benign tumor; however, a few cases have been reported in the past with potential for malignancy. Therefore, the histological nature of papillary adenomas remains controversial. This article presents a rare case of a multifocal papillary adenoma with uncertain malignant potential, featuring an ERBIN-BRAF gene fusion and an APC mutation, along with a literature review, to enhance understanding of this tumor. CASE DESCRIPTION: The patient sought medical consultation due to symptoms of cough and sputum production. Imaging showed a high-density, lobulated nodule in the posterior basal segment of the left lower lobe, surrounded by multiple smaller nodules. Postpulmonary lobectomy, histopathological examination revealed a large nodule composed of a single papillary structure, with the papillary surface covered by a single layer of cuboidal or low-columnar epithelium. Local areas showed transition to surrounding alveolar epithelium, and well-formed glands were observed in the proliferative fibrous tissue, with local stromal fibrosis. Some tumor cells in the surrounding small nodules grew in a lepidic fashion, with cellular morphology similar to that of the large nodule. Immunohistochemical staining showed that tumor cells were positive for TTF-1, CK, CK7, and Napsin A, with a few cells expressing P53 and a Ki-67 index of approximately 8%. Next-generation sequencing (NGS) identified an APC gene mutation (Exon 16, p.E1306∗) and an ERBIN exon3-BRAF exon11 fusion. Given that BRAF alterations have been implicated in lung carcinogenesis, a similar BRAF-mediated tumorigenic pathway may be active in this tumor; therefore, complete resection of the adenoma may be indicated. The tumor's multifocal distribution and molecular alterations suggest that this case represents a papillary adenoma with uncertain malignant potential.

conclusionsCurrently, there is no established standard treatment for such tumors, and the tumor in this case underwent pulmonary lobectomy. Future studies should accumulate more cases to clarify the prognosis and treatment guidelines for this type of tumor.