Histologic transformation of non-small-cell lung cancer in brain metastases

Background Treatment strategies differ substantially for small-cell lung cancer (SCLC), adenocarcinoma and squamous-cell cancer (SCC). Therefore, it is of important significance to identify histologic transformation. There are no reports on histologic transformation in brain metastases (BM) to date. The aim of this study was to analyze the histologic transformation in BM for the first time. Methods Medical records were reviewed and patients with both resected BM and primary tumors were examined retrospectively. The histologic diagnosis was confirmed by H&E staining, and additional diagnostic immunohistochemical stains were performed at the discretion of the pathologists. Characteristics of histologic transformation in BM were analyzed. Results 3 of 24 patients (12.5%) with both resected BM and primary non-small-cell lung cancers (NSCLCs) had evidence of histologic transformation in BM. One case with SCC transformed to adenocarcinoma in brain, one case with adenocarcinoma transformed to SCLC, and another case with adenocarcinoma transformed to SCC. The three cases of histologic transformation were all spontaneous and had not tested gene status. Conclusions We disclosed the histologic transformation of NSCLC in BM at a frequency not as low as expected, and speculated it as an evolution promoted by intratumor heterogeneity, though it warrants further prospective multi-institution investigations with comprehensive molecular analysis. Our findings provided further impetus for surgery when the metastatic or recurrent lesion is resectable, and repeated pathologic evaluation to help tailor individualized treatment.