Immunohistochemical detection of XIAP and p63 in adenomatous hyperplasia, atypical adenomatous hyperplasia, bronchioloalveolar carcinoma and well-differentiated adenocarcinoma

The critical distinction of bronchioloalveolar carcinoma (BAC), well-differentiated adenocarcinoma (WDAC) of lung, adenomatous hyperplasia (AH) and atypical adenomatous hyperplasia (AAH), is based on morphological criteria alone, and is therefore potentially subjective. We examined expression of two markers, X-linked inhibitor of apoptosis protein (XIAP), the most potent of the inhibitor of apoptosis protein (IAP) family, and p63, a marker of bronchial reserve cells (BRC) and squamous cells, in these entities. H&E slides of 37 tissue blocks from 27 patients were reviewed and classified as AH (n = 7), AAH (n = 8), BAC (n = 9) and WDAC (n = 13). Immunostaining was performed on 4 mu m sections with monoclonal anti-XIAP and monoclonal anti-p63. Granular or heterogeneous cytoplasmic staining for XIAP and nuclear staining for p63 were considered positive. Neither XIAP nor p63 were detected in normal lung alveolar cells. All seven AHs were negative for XIAP and negative or focally positive for p63. All eight AAHs were positive for XIAP and displayed p63 positivity in scattered cells. All BACs displayed XIAP positivity, which ranged from focal/weak to diffuse/strong. p63 was negative in seven and focally positive in two of nine BACs. Twelve of 13 WDACs showed XIAP positivity in a similar pattern to BAC; all were negative for p63. One aberrant case diagnosed on H & E as WDAC was negative for XIAP but strongly positive for p63. Significant XIAP expression appears to be useful for distinguishing AAH from AH. Commonality of XIAP staining in AAH, BAC and WDAC supports the possibility that AAH may be a premalignant lesion. The rarity of p63 expression confirms previous reports and supports a nonbronchial histogenesis of these entities. In contrast, diffuse p63 staining may facilitate the identification of rare cases that may have been misclassified as alveolar in origin based on morphology but may be of BRC origin.