PERIPHERAL PULMONARY ADENOCARCINOMAS WITH BRONCHIOLOALVEOLAR FEATURES- IMMUNOPHENOTYPES CORRELATE WITH HISTOLOGIC PATTERNS

Peripheral pulmonary adenocarcinomas (PPAs) often demonstrate a bronch ioloalveolar component, with Or without glandular differentiation. PPA s can be nondescript, mucinous, or show features of Type II pneumocyte s, Particularly, mucinous lung carcinomas can resemble gastrointestina l metastases, Previous reports suggested that patterns of keratins 7 ( K7) and 20 (K20) differ in pulmonary tumors versus enteric metastases. These studies, however, often failed to specify the precise morphotyp es of PPA. Thus, we undertook this evaluation of PPAs with different h istologic images. Thirty-nine cases were retrieved from institutional files; all were confirmed as primary tumors by clinicopathologic and r adiographic review. Cases were classified as Type I (mucinous) bronchi oloalveolar carcinoma (BAC1); Type II (nonmucinous) bronchioloalveolar carcinoma (BAC2); conventional PPA with BAC1-like areas (PPA1); or co nventional PPA with BAC2-like foci (PPA2). Immunostains were performed for K7, K20, carcinoembryonic antigen, CA19-9, tumor-associated glyco protein-72, surfactant apoprotein-A, and the c-erbB-2 peptide. BAC1 an d PPA1 failed to express surfactant apoprotein-A, and BAC2 also consis tently lacked K20, whereas 28% of PPA2 lesions were labeled for K20, A ll of the other determinants, however, were seen in variable proportio ns in each subgroup of PPA. Primary BAC1 and PPA1 resembled enteric ad enocarcinomas immunophenotypically; on the other hand, BAC2 demonstrat ed a pattern of protein expression similar to that of Type II pneumocy tes. PPA2s are a diverse group of neoplasms, and a subset of PPA2 does show K20 reactivity, as would be expected in metastatic enteric carci nomas. Thus, immunohistochemical data on PPAs must be interpreted care fully and only in clinicopathologic context. With respect specifically to primary pulmonary mucinous tumors, there still seems to be no unif ormly reliably marker that will always allow the exclusion of metastat ic enteric tumors.