71
Pulmonary Atypical Adenomatous Hyperplasia And BronchioloalveolarCarcinoma
Meilin Xu Xia Yang Zhiyao Zhang
OBJECTIVE To study the relationship between atypicat adenomatous hyperplasia (AAH) and bronchioloalveolar carcinoma (BAC).
METHODS Morphometric, immunohistochemical and ultrastructural analyses were performed in 4 patients with low grade AAH, 5 with high grade AAH and 7 with BAC.
Department of Pathology,Tianjin Chest
RESULTS The mean nuclear areas of high grade AAH and BAC were greater
Hospital, Tianjin 300051, China.
than those of low grade AAH (P<0.05); p53 protein expression was negative in 4 cases of low grade AAH,while the positive rates in high grade AAH and BAC were 40% (2/5) and 57% (4/7), respectively.
Correspendence to: Meilin Xu
CONCLUSIION The development of BAC is stepwise. AAH appears to be a lesion closely related with BAC, probably as its genuine precursor.
KEYWORDS:lung,atypicaladenomatoushyperplasia,bronchioloalveolalung carcinoma,p53 protein,electronmicroscopy. ung cancer is the most common malignancy in humans. Among
L the various histologic types of lung cancer, adenocarcinoma is one of the main types. A recent study indicated that adenocarcinoma had displaced squamous carcinoma as the most common pulmonary carcinoma m. Bronchioloalveolar carcinoma (BAC) is a specific form of lung adenocarcinoma, different from the ordinary adenocarcinomas in three subtypes: mucoepithelial, bronchioloepithelial and inflammatory-sclerosing. Histologically, BAC is defined by tumor cell growth along pre-existing alveolar structures.BAC exhibits unique histogenosis and morphologic features distinguishing it from bronchogenic adenocarcinoma. For early detection, therapy and prevention of BAC, it is essential to study its histogenesis and pathogenesis. Kitamura et al. [21 reported that the development of BAC appears to be stepwise. Atypical adenomatous hyperplasia (AAH) is morphologically similar to BAC. AAH cells share many biologic properties with BAC ceils, including certain genetic abnormalities.It has been suggested that AAH is a putative precursor or even early-stage lesion of BAC 1:~-8].Sofar, however, direct evidence that AAH cells develop into BAC cells is lacking. Cytomorphologic and biologic characteristics of AAH and BAC cells were studied through hospital files based on recent references in the literature to evaluate the relationship between AAH and BAC and the possibility of AAH as a precursor of BAC.
MATERIALS AND METHODS Specimen classification criteria Received February 11, 2004; accepted April 9, 2004. Chinese Journal of Clinical Oncolgy Email:
[email protected] Tel(Fax):0086-022-23522919
In this study, all the lung specimens were selected from Tianjin Chest
72 ChineseJournal of Clinical Oncology 2004/Volume 1/Number I
Hospital between 1990 and 1999. They were diagnosed and classified into 7 BAC lesions,4 low-grade AAH lesions, and 5 high-grade AAH lesions. The low and high grade atypical AAH lesions were identified using the criteria of Kitamura et al i21. In AAH showing low-grade atypia, the density of cells was low, and the cells were arranged in a single layer, either intermittently or continuously, on the alveolar septum. The nuclei were small showing minimal variations in size, shape and chromaticity (Fig. 1). In AAH showing high-grade atypia, the density of cells was high, and the nuclei were larger, exhibiting greater variations in size, shape and chromaticity(Fig. 2).
RESULTS Pathology On gross examination, the AAH lesions were usually recognized as small ones on the cut surface of the lung. In 9 specimens, the lesions were only several millimeters in maximal diameter, white or gray-white, with a distinct margin. Within the lesion, alveolar structure could be recognized. On bistologic examination, cuboid or low-columnar cells resembling Clara cell or type ]I alveolar cells were seen along the alveolar septa. Due to fibrosis or lymphocytic infiltration, the alveolar septa were slightly thickened, but no interstitial scar formation was observed. The AAH cells showed various degrees of cellular atypical hyperplasia, such as nuclear hyperchromasia, enlargement, irregularity, pleomorphism, prominent nucleoli, hypercellularity, and disarray in cell arrangement, however, the degree of atypia was generally mild to moderate. Binucleated and multinucleated cells were occasionally seen.As in BAC cells, inclusions were frequently observed in AAH cells.
Morphometry
Fig. 1. The low-grade AAH cells were arranged on the alveolar septa.The nuclei were small and showed minimal variations in size, shape,and chromaticity (x400).
Using the software package for micro-imaging analysis, the nuclear areas of AAH and BAC cells were measured. The mean nuclear areas in high-grade AAH and BAC were markedly larger than those in l o w grade AAH, with significant differentces (P<0.05) (TableD. Table 1. Mophometric measurements of AAH cells and BAC cells
Fig. 2. The high-grade AAHs exhibited higher cell density. Their nuclei were larger and showed greater variations in size,shape, and chromaticity (x400).
StatisticalAnalysis The mean and standard deviation of the mean (mean_+ SD) were calculated for measuring data. A t test that revealed P<0.05, indicated a significant difference.
Lung lesions
n
Mean nucleararea(t.un2)
Low-grade AAH
4
31.0_+6.4
High-grade AAH
5
45.2+_6.4
Low-grade AAH
4
31.0+_6.4
BAC
7
55.8+_15.6
High-grade AAH
5
45.2+_6.4
BAC
7
55.8+_15.6
l 3.31"
2.98* 1.42
*P<0.05
Immunohistochemistryand Uitrastructure Immunohistochemistry staining of AAH cells and BAC cells was performed using the mouse monoclonal p53 antibody. The results showed that p53-protein accumulation was not identified (0%) in any of the 4 low-grade AAHs, in 2 (40%) of the 5 high-grade AAHs, and in 4(57%) of the 7 BACs (Table 2, Fig.3).
Adenomatous hyperplasia and bronchioloalveolar carcinoma/Meilin Xu et al.
73
Table 2. The level of p53 expression in the A A H cells and B A C cells
Lung lesions
p53 protien +
n
Frequency of positive cells(%)
Ix)w-grade AAH
0
4
4
0
High-grade AAH
2
3
5
40
BAC
4
3
7
57
Fig. 5. The type 1I cells of BAC showed irregula," nuclei and difterent stage lamellar bodies (x6000).
DISCUSSION
Fig. 3. The BAC cells show lligh-level p53 expression.
The ultrastructural results showed that many inclusions consisting of lamellar bodies and branching microtubular structures were frequently observed in AAH cells (Fig.4). These results indicated that AAH cells differentiated predominantly toward type H cells. BAC cells retain this feature, but to a lesser extent. Cells with Clara-cell differentiation were apparent and tended to increase in the progression from early-stage BAC to overt BAC(Fig.5).
Fig. 4. Many lamellar bodies and inclusions consislJng of branching microtubular structures were frequently observed in AAH cells
(x5000).
Atypical adenomatous hyperplasia (AAH) was defined as a small lesion with proliferation of cttboid or lowcolumnar cells along the alveolar septa. The AAH lesion has also been given other nomenclature, such as atypical alveolar (or alveolar atypical) cell hyperplasia, atypical bronchioloalveolar cell hyperplasia, bronchiCoalveolar epithelial hyperplasia, and bronchioloalveolar cell adenoma I3'9-~'51.Different choices of definition might reflect different knowledge of the same lesion by scholars. Some believe that the lesions are only regenerative proliferation after injury. Bcause of destruction of alveolar structures inducing AAH, and resulting in development of BAC, others recognise !hat AAH lesions are putative precursors of malignancy. Morphometric analyses of nuclear areas have been used for a number of neoplastic and tumor-like lesions. Morphometric studies of AAH and BAC demonstrated that the mean nuclear area was > 50p~mz in the cells of BAC, and < 50txm2 in the cells of AAH (Tablel). It was important to combine the consideration of lesion size and mean nuclear area. Kitamura e t al 12j.Suggested the effective cutoff values for distinguishing AAH from early-stage BAC: 40p,m 2 for the mean nuclear area, and 5mm for the lesion size. Miller LaLproposed that a "bronchioloalveolar cell tumor" > 5ram and showing marked nuclear atypia be classified as BAC. The results in this study was compatible with that of Kitamura' s. These morphometric parameters and data are scientifically significant and of useful value in distinguishing AAH from early-stage BAC, but further careful studies are required to establish definite diagnostic criteria. Ultrastructural investigation showed appearance of cells with Clara-cell differentiation and increasing in
74
Chinese Journal of Clinical Oncology 2004/Volume 1/Number I genase 2(COX-2) expression occurs frequently in precursor
the progression of lesions from e a r l y - s t a g e BAC to overt BAC. It appears that such differentiation may
lesions of human adenocarcinoma of the lung. Lung Cancer,
reflect metaplasia appearing in tumor cells during the development of BAC. Further studies are needed to examine the expression of various SP subtypies (A,B,C) in the cells of AAH and BAC using immunohistochemistry and in situ hybridization. The cells of BAC show many unique morphologic
2000;30:73-81. 5
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that derive from metaplasia and atypical hyperplasia of bronchiolar epithelial cells. The precise site, cell type of origin, the histogenesis of BAC, and the precursor of BAC have long been controversial El-ttl. However, increasing evidence suggests that AAH is a genuine precursor of BAC. In multiple stages and steps, BAC most likely develop from l o w - g r a d e AAH to h i g h grade AAH to early-stage (or in situ) BAC to infiltrative (or advanced) BAC. The lesions of AAH and BAC represent a continuous developmental process of bron-
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