Atypical adenomatous hyperplasia of the lung. Implications for the pathogenesis of peripheral lung adenocarcinoma

Bronchioloalveolar lung carcinoma (BAC) exhibits many features that distinguish it from bronchogenic carcinomas. For early detection, therapy, and prevention of BAC, it is essential to understand its pathogenesis. Development of BAC appears to be stepwise, and the earliest lesion to be recognized is atypical adenomatous hyperplasia (AAH), the proliferative lesion of atypical epithelial cells along the alveolar septa. Our review of the studies of AAH revealed that certain populations of AAH cells exhibit active proliferation, aneuploidy, 3p and 9p deletions, K-ras codon 12 mutation, and disruption of the cell cycle control, but p53 gene aberrations are rare and telomerase activation is absent. We emphasize that AAH is an alveolar intraepithelial neoplasia. This allows more precise analyses of the process and mechanism of the development of BAC. Furthermore, AAH could serve as a surrogate end-point biomarker in future chemoprevention trials. The criteria for the diagnosis of AAH and related lesions should be established as early as possible.     

Atypical adenomatous hyperplasia of the lung: a probable forerunner in the development of adenocarcinoma of the lung.

An increasingly large body of work suggests that atypical adenomatous hyperplasia (AAH) of the lung may be a forerunner of pulmonary adenocarcinoma. Recognizing this fact, the World Health Organization now acknowledges the existence of AAH while noting difficulties that may be encountered in distinguishing AAH from the nonmucinous variant of bronchioloalveolar carcinoma. Regrettably, a universally acceptable definition of morphologic criteria for the diagnosis of AAH has not been achieved. This review of the literature examines the epidemiology, gross appearance, light microscopic findings, morphometry, immunohistochemistry, and molecular features of AAH and suggests a set of histopathologic features that may help the practicing pathologist identify this intriguing lesion. These features include the following: irregularly bordered focal proliferations of atypical cells spreading along the preexisting alveolar framework; prominent cuboidal to low columnar alveolar epithelial cells with variable degree of atypia but less than that seen in adenocarcinoma; increased cell size and nuclear-cytoplasmic ratio with hyperchromasia and prominent nucleoli, generally intact intercellular attachment of atypical cells with occasional empty-looking spaces between them without high cellularity and without tufting or papillary structures; and slight thickening of the alveolar walls on which the AAH cells have spread, with some fibrosis but without scar formation or significant chronic inflammation of the surrounding lung tissue. Several lines of evidence indicate that AAH is a lesion closely associated with adenocarcinoma of the lung, suggesting AAH may be involved in the early stage of a complex multistep carcinogenesis of pulmonary adenocarcinoma.     

Pulmonary preinvasive neoplasia

Advances in molecular biology have increased our knowledge of the biology of preneoplastic lesions in the human lung. The recently published WHO lung tumour classification defines three separate lesions that are regarded as preinvasive neoplasia. These are (1) squamous dysplasia and carcinoma in situ (SD/CIS), (2) atypical adenomatous hyperplasia (AAH), and (3) diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIP-NECH). SD/CIS is graded in four stages (mild, moderate, severe, and CIS), based upon the distribution of atypical cells and mitotic figures. Most airways showing SD/CIS demonstrate a range of grades; many epithelia are hard to assess and the reproducibility of this complex system remains to be established. Detailed criteria are, however, welcome and provide an objective framework on which to compare various molecular changes. Alterations in gene expression and chromosome structure known to be associated with malignant transformation can be demonstrated in CIS, less so in dysplasias, but also in morphologically normal epithelium. The changes might be sequential, and their frequency and number increase with atypia. Less is known of the "risk of progression" of SD/CIS to invasive "central" bronchial carcinoma. It may take between one and 10 years for invasion to occur, yet the lesion(s) may be reversible if carcinogen exposure ceases. AAH may be an important precursor lesion for peripheral "parenchymal" adenocarcinoma of the lung: the "adenoma" in an adenoma-carcinoma sequence. There is good morphological evidence that AAH may progress from low to high grade to bronchioloalveolar carcinoma (BAC; a non-invasive lesion by definition). Invasion then develops within BAC and peripheral lung adenocarcinoma evolves. The molecular events associated with this progression are not well understood and studies are hampered by a lack of clear criteria to distinguish high grade AAH from BAC. Nonetheless, as with SD/CIS, the patterns of expression of tumour associated genes are consistent with neoplastic progression. We have little idea of the incidence of AAH in the normal or "smoking" populations. It is found more frequently in cancer bearing lungs, especially in those with adenocarcinoma, and is more common in women. No data are available on the risk of progression of AAH. DIPNECH is an exceptionally rare lesion associated with the development of multiple carcinoid tumours. Almost nothing is known of its biology. Knowledge of these lesions will be crucial in the design and understanding of lung cancer screening programmes, where it is likely that the morphological and, more importantly perhaps, the molecular characteristics of these lesions will provide useful targets for detection and possibly even treatment.     

表皮生长因子受体与肺泡上皮不典型腺瘤样增生的关系

肺癌是人类常见的恶性肿瘤,肺腺癌是其主要类型之一.细支气管肺泡癌(bronchioloalveolar lung carcinoma,BAC)是肺腺癌的一个特殊类型.肺泡上皮不典型腺瘤样增生(atypical adenomatous hyperplasia,AAH)可能是BAC或腺癌的癌前病变,甚至是其早期癌.表皮生长...     

A case of double primary adenocarcinoma of the lung with multiple atypical adenomatous hyperplasia

A case of double primary adenocarclnoma of the lung with multiple atypical adenomatous hyperplasla (AAH) In a 77-year-old woman Is reported. Hlstopathologlcally, in the resected left upper lobe of the lung, both cancers were diagnosed as well-differentlated papillary adenocarcinoma, and 161 lesions of AAH were also found. Both the cancer lesions and six AAH (greater than 3 mm In diameter) were examined wlth regard to immunoreactivity of carcinoem-bryonlc antigen (CEA) and p53 gene product, microsatellite lnstabllity (MI) and loss of heterozygosity (LOH) on chromosome 9q and 17q by polymerase chain reaction (PCR). Although both cancers expressed CEA, they did not show clonal lmmunoreactivity for the p53 gene product. Atypical adenomatous hyperplasia expressed CEA weakly and showed no immunoreactlvity for p53 gene protein. Both carcinomas showed LOH on chromosome 17q, and one of them showed LOH on chromosome 9q. In six AAH, LOH on chromosome 17q was detected In two tumors, and one of them also showed LOH on chromosome 9q. One AAH, which was negative for LOH on chromosome 17q and 9q, showed Mi at D17S791. These results indicated that AAH is a clonal neoplastic lesion with genetic abnormalities and should be called intraepithelial pneumocyte neoplasia, and that each of the numerous papillary lesions in this case was considered to be an Independent lesion.     

Monoclonality of Atypical Adenomatous Hyperplasia of the Lung

Atypical adenomatous hyperplasia (AAH) of the lung has been postulated as a possible precursor lesion of bronchioloalveolar carcinoma (BAC). The clonality of AAHs from seven female patients was analyzed to determine whether AAH is a monoclonal expansion. All AAHs were identified in lungs surgically resected for BAC. The clonality of the BAC and bronchiolar metaplasia in each case was also analyzed. Approximately 500 cells in each lesion were precisely microdissected from methanol-fixed sections. Adjacent normal lung tissue was collected as a normal control. DNA was extracted for clonal analysis based on an X-chromosome-linked polymorphic marker, the human androgen receptor gene (HUMARA). HUMARA was found to be amplified with or without previous digestion by the methylation-sensitive restriction endonuclease HpaII. Five cases were informative. All 10 AAHs and 7 BACs obtained from the informative cases showed monoclonality, whereas the control cells showed polyclonality. Three different AAH lesions in a single case showed both possible patterns of monoclonality. BAC and contiguous AAH showed identical monoclonality in two cases. Two lesions of bronchiolar metaplasia, which was considered reactive, were polyclonal. Our results demonstrated the monoclonal nature of AAH, and this finding suggests that AAH is a precursor of BAC or a preneoplastic condition.     

Cytodifferentiation of atypical adenomatous hyperplasia and bronchioloalveolar lung carcinoma: immunohistochemical and ultrastructural studies

We used immunohistochemistry and electron microscopy to evaluate the differentiation of cells comprising atypical adenomatous hyperplasia (AAH; n = 26), early bronchioloalveolar lung carcinoma (BAC; n = 11), and overt BAC (n = 16), which are assumed to constitute a continuous spectrum of developmental steps of BAC. Surfactant apoprotein (SAP), a marker for type 2 alveolar cells, was expressed in cells from all the lesions of AAH, early BAC, and overt BAC. However, the proportion of SAP-positive cells decreased and their distribution became more heterogeneous with advancing lesion grade. Urine protein 1, which is identical to the Clara cell-specific 10 kDa protein, was expressed in 70% of overt BAC, whereas only 20% of early BAC showed weak reactivity and none of AAH lesions showed any reactivity at all. Ultrastructurally, type 2 alveolar cell differentiation was predominant among cells from AAH and early BAC. Our results suggest that precursor cells of BAC differentiate predominantly towards type 2 alveolar cells. Cells comprising overt BAC retain this differentiation phenotype, but to a reduced extent. In contrast, concomitantly with progression, cells with Clara cell differentiation emerge and their proportion increases. Such phenotypic changes may reflect metaplasia occurring in tumour cells during the development of BAC.     

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 mum 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 pre-malignant 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.     

Comparative Ultrastructural Study of Atypical Adenomatous Hyperplasia and Adenocarcinoma of the Human Lung

Atypical adenomatous hyperplasia (AAH) of the human lung is considered a possible precursor of pulmonary adenocarcinoma. However, its true biological significance remains to be clarified. The authors studied the ultrastructure of AAH in surgically resected lungs and compared it with that of coexisting adenocarcinoma in an effort to define the characteristic features of AAH. Ultrastructurally, AAH possessed oval to irregular nuclei with high nucleo-cytoplasmic ratio and large nucleoli. Development of cytoplasmic organelles was generally poorer in AAH than in adenocarcinoma. However, these differences became less apparent as the degree of atypia of AAH advanced. Both lamellar bodies and electron-dense granules were found in AAH as well as in adenocarcinoma. These results suggest a close relation of AAH with adenocarcinoma of type 2 pneumocyte or Clara cell type. Further, the results of immunohistochemical studies for surfactant apoprotein A, urine protein 1, cytochrome P-450s, CEA, p53, c-erbB-2, Ki67, and bcl-2 well reflected the ultrastructural findings. These results suggest, in accordance with previous studies, that AAH is a lesion closely related to adenocarcinoma. Further, AAH shares some characteristics of type 2 pneumocytes and Clara cells, implying that it might be derived from their common precursor.     

Lung adenocarcinoma with bronchioloalveolar carcinoma component is frequently associated with foci of high-grade atypical adenomatous hyperplasia

We assessed the occurrence of atypical adenomatous hyperplasia (AAH) in whole lung lobes with primary cancer lesions. Following surgical resection, tissue specimens were sliced to a thickness of 4 mm (3,641 specimens from 61 cases; mean = 59.7 specimens per case). A total of 119 AAH foci were found and an association was evident in 25 (57%) of 44 adenocarcinomas, 3 (30%) of 10 squamous cell carcinomas, and 2 (29%) of 7 other lung cancers. Histologic evaluation showed that 108 AAH foci were categorized as low-grade and the other 11 as high-grade AAH. These 11 foci of high-grade AAH were present in 7 patients with adenocarcinoma, and in 1 patient there was a synchronous double primary lung adenocarcinoma. High-grade AAH was closely associated with bronchioloalveolar carcinoma (BAC) type adenocarcinoma, and low-grade AAH with non-BAC adenocarcinoma. The mean +/- SD Ki-67 labeling index in high-grade AAH (3.5%+/-2.9%) was significantly higher than for the low-grade index (1.4%+/-1.6%). We propose that foci of high- but not low-grade AAH may be potential precursor lesions of lung adenocarcinoma, especially with the BAC component.     

Lung adenocarcinoma associated with familial adenomatous polyposis. Clear cell carcinoma with beta-catenin accumulation accompanied by atypical adenomatous hyperplasia

A 46-year-old man presented with a lung tumor 17 years after a subtotal colectomy and 13 years after a partial duodenectomy for familial adenomatous polyposis (FAP). There had been no malignant transformation in the specimens from his colectomy and duodenectomy, and a current gastrointestinal investigation revealed no evidence of malignancy. Pathological analysis of the lung tumor demonstrated adenocarcinoma with clear cells and a papillary structure, accompanied by tiny tumorous nodules in the background lung parenchyma. Many of the nodules were multifocal adenocarcinoma; however, some of the nodules demonstrated atypical adenomatous hyperplasia (AAH). This is the first case report of a lung adenocarcinoma accompanied by AAH in a FAP patient. Immunohistochemical and loss of heterozygosity studies revealed unique features of the lesions reflecting a disruption of the adenomatous poliposis coli–beta-catenin pathway.     

Molecular alterations in atypical adenomatous hyperplasia occurring in benign and cancer-bearing lungs.

Atypical adenomatous hyperplasia (AAH) is considered to be a precursor lesion of the lung adenocarcinoma. Several genetic abnormalities have been reported in AAH associated with adenocarcinoma, but little is known about AAH associated with benign lung lesions. To address this we compared the molecular characteristics of AAH present in benign conditions to those coexisting with carcinoma. Seven cases of AAH from resected non-neoplastic lungs (AAH-B) and 12 cases from lungs resected for primary lung carcinoma (AAH-M) were analyzed for loss of heterozygosity (LOH) using 21 polymorphic microsatellite markers situated in proximity to known tumor suppressor genes on chromosomes 3p, 5q, 7p, 9p, 10q, and 17p. Direct DNA sequencing for K-ras mutation was also performed. There was a broad range of LOH in both groups. No LOH was identified in 3 cases (25%) of AAH-M, but all cases of AAH-B showed LOH (P=0.26). Six cases (50%) of AAH-M and 3 cases (43%) of AAH-B showed loss at 1 marker (P=0.99). LOH at 2 or more markers was identified in 3 (25%) cases of AAH-M and 4 (57%) cases of AAH-B (P=0.32). LOH was most frequently detected on chromosomes 3p and 10q in both groups. The difference in overall fractional allelic loss between the 2 groups did not reach statistical significance. K-ras mutations were not identified in either group. Our results showed a significant overlap in LOH patterns between AAH with or without coexistent lung malignancy. Therefore, AAH may represent a smoking induced low-grade neoplastic lesion that may be a precursor lesion of only a subset of invasive lung adenocarcinoma.     

A subset of lung adenocarcinomas and atypical adenomatous hyperplasia-associated foci are genotypically related: an EGFR, HER2, and K-ras mutational analysis

Atypical adenomatous hyperplasia (AAH) is considered the preinvasive lesion of pulmonary adenocarcinoma, and mutations of EGFR, HER2, and K-ras are involved in the early stage of lung adenocarcinoma carcinogenesis, also predicting clinical response to anti-EGFR small molecule inhibitors. We analyzed 18 cases of primary lung adenocarcinoma with concomitant AAH foci from 13 patients for mutations of EGFR (exons 18-21), HER2 (exons 19-20), and K-ras (exon 2) by direct sequencing polymerase chain reaction. Among mutated cases, concordant mutations of EGFR or K-ras in adenocarcinoma and related AAH were observed in 5 (63%) of 8 cases. In particular, 3 of 4 adenocarcinomas with EGFR mutations (all L858R point mutations in women, never or former smokers) had a concomitant and identical mutation in AAH, and 2 of 4 adenocarcinomas with K-ras mutations (both at codon 12 in women, a never and a current smoker) showed the same mutation in concomitant AAH. All cases were wild-type for HER2. Mutations of EGFR and K-ras genes represent an early event in lung adenocarcinomagenesis, and AAH convincingly seems to be a precursor lesion in a subset of cases of adenocarcinoma.     

Argyrophilic nucleolar organizer regions and alpha-fetoprotein in adenomatous hyperplasia in human cirrhotic livers.

Recently, adenomatous hyperplasia (AH) of the liver has been suspected as a precancerous lesion in human hepatocarcinogenesis. The authors examined 75 cases of AH from 42 cirrhotic livers, using staining of argyrophilic nucleolar organizer regions (AgNORs). These reflect proliferative cell activity. Findings in AH were compared with those seen in hepatocellular carcinoma (HCC) and other chronic liver diseases. Expression of alpha-fetoprotein (AFP) was also examined immunohistochemically. The authors classified AH into three types: ordinary (OAH), atypical (AAH), and AH with focal malignancy (FM). OAH implies a lack of atypia; AAH represents AH with structural and cellular atypia but without the features of overt carcinoma; and FM denotes AH with foci of overt HCC. Forty of the 75 cases of AH were categorized as OAH, 19 as AAH, and 16 as FM. The noncancerous areas of FM had features of AAH. The mean number of AgNORs in AH was intermediate between that seen in cirrhosis (2.93) and HCC (6.18) and showed a step-wise increase in the following order: OAH (2.95), AAH (3.89), noncancerous areas in FM (4.58), and malignant foci in FM (5.71). There was no significant difference in AgNOR counts between OAH and cirrhosis. AgNOR counts in AAH and FM were significantly higher than those of OAH, and lower than those of HCC. AFP was positive in 12 of 25 HCCs and in malignant foci of 3 FM lesions, but it was absent in OAH and AAH. These data suggest that OAH has a limited capacity for proliferation but that AAH and FM are much more replicative. The latter two conditions are probably preneoplastic lesions or early forms of HCC.     

Bronchioloalveolar neoplasia

Bronchioloalveolar carcinoma (BAC) arising in the peripheral lung is the prototype of human lung adenocar-cinoma and is considered to develop, at least in part, from its precursor atypical adenomatous hyperplasia (AAH). Molecular genetics investigations have revealed the significant roles of mutations in KRAS and epidermal growth factor receptor (EGFR) genes in the pathogenesis of AAH and BAC. Recently, selective molecular targeting therapies, such as those using EGFR tyrosine kinase inhibitors, have been introduced with remarkable success. In spite of the accumulation of research results into BAC/AAH, there remain three important issues to be addressed; 1) the etiology of BAC and AAH, 2) the genetic and/or epigenetic alteration(s) responsible for the progression of AAH to BAC, 3) the genetic backgrounds speculated as the cause of multiple AAH/BAC. These three issues are briefly reviewed and discussed, along with the murine pulmonary carcinogenesis model which is potentially useful for solving these issues.     

Bronchioloalveolar neoplasia

Bronchioloalveolar carcinoma (BAC) arising in the peripheral lung is the prototype of human lung adenocar-cinoma and is considered to develop, at least in part, from its precursor atypical adenomatous hyperplasia (AAH). Molecular genetics investigations have revealed the significant roles of mutations in KRAS and epidermal growth factor receptor (EGFR) genes in the pathogenesis of AAH and BAC. Recently, selective molecular targeting therapies, such as those using EGFR tyrosine kinase inhibitors, have been introduced with remarkable success. In spite of the accumulation of research results into BAC/AAH, there remain three important issues to be addressed; 1) the etiology of BAC and AAH, 2) the genetic and/or epigenetic alteration(s) responsible for the progression of AAH to BAC, 3) the genetic backgrounds speculated as the cause of multiple AAH/BAC. These three issues are briefly reviewed and discussed, along with the murine pulmonary carcinogenesis model which is potentially useful for solving these issues.     

Expression patterns of type II pneumocyte apical surface glycoconjugates in lung adenocarcinoma cells

 Monoclonal antibodies and lectins were used to examine the expression patterns of apical membrane oligosaccharide sequences specific to type II pneumocytes in atypical adenomatous hyperplasia (AAH) and lung cancer. Atypical cells of AAH and papillary adenocarcinoma cells expressed abundant sialyl Thomsen-Friedenreich (TF) antigen: this was not observed in acinar adenocarcinoma, bronchioloalveolar carcinoma with mucin production or squamous cell carcinoma. Sialyl Tn antigens was also detected on a few cells in AAH and papillary adenocarcinomas. Asialo TF and Tn antigen were not observed on the surface of carcinoma cells of any type. Alpha(α)2,3-linked sialic acids predominated in type II pneumocyte, AAH and papillary adenocarcinoma, whereas ciliated columnar cells expressed α2,6-linked sialic acids. Lewis^x and sialyl Lewis^x antigens capped the TF antigen in both O- and N-linked side chains on the surface of AAH and papillary adenocarcinoma cells, but were not expressed by type II pneumocytes. The findings demonstrate that papillary adenocarcinoma cells resemble type II pneumocytes in that they express abundant sialyl TF surface antigen, but they also express TF-related antigens not found in type II pneumocytes. Apical surface glycoconjugates of AAH have structural characteristics shared by both type II pneumocytes and papillary adenocarcinoma cells. Received: 6 July 1998 / Accepted: 25 September 1998     

Expression of cyclin D1, retinoblastoma gene protein, and p16 MTS1 protein in atypical adenomatous hyperplasia and adenocarcinoma of the lung

 To clarify the events leading to the disruption of cell growth control that occurs during the development of pulmonary adenocarcinoma (AC), we used immunohistochemistry to evaluate the expression of G1 cycle regulators, cyclin D1, Rb protein (pRb), and p16 MTS1 protein and the tumour proliferation marker, Ki 67, both in AC of the lung and in its precursor lesion, atypical adenomatous hyperplasia (AAH). The frequency of lesions with cyclin D1 overexpression was relatively high in AAH (47–89%), but was decreased in early AC (28%) and overt AC (35%). The loss of pRb expression was rare in both AAH (0–18%) and early AC (0%), and was infrequent even in overt AC (13%). The loss of p16 expression was also relatively infrequent in both the premalignant and the malignant lesions (11–25%). Our results suggest that overexpression of cyclin D1 is an early event and plays an important part in tumorigenesis in the case of lung AC. However, cyclin D1 overexpression is not required for the development and maintenance of a malignant phenotype. It is likely that some cyclin D1-independent pathways other than Rb and p16 abnormalities have an important role in the malignant transformation from AAH to early AC. Received: 8 July 1997 / 26 September 1997