Comparative mutational analysis of pulmonary scar epithelium, bronchioloalveolar carcinomas, and invasive well-differentiated pulmonary adenocarcinomas: a molecular approach to diagnostically challenging cases.

Discrimination of invasive well-differentiated adenocarcinoma (IAD) from reactive bronchioloalveolar epithelium entrapped in pulmonary scars (PSE) may be difficult on routine histology, especially on small biopsies. Ancillary studies to help in this regard are desirable. Whereas IADs have been shown to harbor cumulative mutational damage of tumor suppressor genes, little is known about molecular changes in PSEs. In this study, we compared cumulative loss of heterozygosity (LOH) of tumor suppressor genes in PSEs (N = 12), bronchioloalveolar carcinomas (BACs, N = 15) and stage 1 IADs (N = 7). Unstained serial sections were microdissected to obtain lesional and normal tissue DNA. PCR was performed for up to 16 polymorphic markers. An allelic ratio of < 0.5 or >2.0 was designated as LOH. Fractional allelic loss (FAL) was calculated for each case as the number of markers with LOH divided by the total number of informative markers. Mean percentage of informative markers was 76.8%. PSEs showed significantly lower mean FAL compared with BACs and IADs (3.0% vs. 20.4% and 28.5%, respectively; P < 0.003). Only 1 case of PSE showed LOH of one marker in two different areas, whereas the majority of allelic losses in the neoplasms were present in two or more microdissected foci. Our study shows that PSEs harbor LOH of tumor suppressor genes at relatively low rates and in a random distribution compared with BACs and IADs, which show consistent allelic losses, and high FALs. These molecular differences may serve as an adjunct to histology in challenging glandular lesions of the lung.

p63 expression in assessment of bronchioloalveolar proliferations of the lung.

Discrimination of well-differentiated pulmonary adenocarcinoma from reactive bronchioloalveolar epithelium can be difficult on routine histology, especially with small biopsies. Ancillary studies to help in this distinction are desirable. p63, a p53-homologous nuclear protein, is a marker of reserve cells of the bronchus and terminal lobular unit. In this study, 33 cases of adenocarcinoma (20 open lung and 13 transbronchial/percutaneous biopsies) and 43 cases of benign lungs with fibrosis and metaplasia (22 open lung and 21 transbronchial/percutaneous biopsies) were studied for nuclear p63 expression by immunohistochemistry (Dako, Carpinteria, CA, USA). Five additional cases each of atypical adenomatous hyperplasia and adenosquamous carcinoma and three cases of squamous carcinoma (all open lung biopsies) were also stained. The diagnostic categories of benign lung conditions were usual interstitial pneumonia, parenchymal scar, cryptogenic organizing pneumonia and diffuse alveolar damage. In neoplastic cases, p63 positivity was calculated as percentage of all tumor cells examined. In areas of normal lung, p63 decorated the reserve cells of large and small airways and occasional cells of the distal lobular unit. In fibrotic reactive processes, an interrupted but distinct pattern of nuclear staining was present in all cases, with staining of basal cells of the airways as well as bronchiolar- and squamous-metaplastic epithelium (43/43, 100%). p63 immunoreactivity was less uniform in areas of acute lung injury within these cases. One adenocarcinoma and two cases of atypical adenomatous hyperplasia showed strong immunoreactivity (>80%), while three adenocarcinomas highlighted only rare tumor nuclei (<5% of tumor cells). Morphologic areas where p63 immunostaining was not helpful included the junction of normal lung and lepidic growth of adenocarcinoma, and retrograde spread of adenocarcinoma into small airways. Our results highlight the differential expression of p63 across various bronchioloalveolar lesions. Moreover, p63 may be helpful in distinguishing reactive from neoplastic glandular proliferations in the lung.

Molecular genotyping of medullary thyroid carcinoma can predict tumor recurrence.

Medullary thyroid carcinoma can have an aggressive behavior, and little is known about the molecular basis for clinical outcome. Defining risk of recurrent or metastatic disease is difficult, and it has been limited to clinical and pathologic features, such as advanced age, cervical lymph node metastases, and stage at presentation. Using microdissection and genotyping, we studied 11 cases of medullary carcinoma for allelic losses in a panel of known tumor suppressor genes. The tumor suppressor genes with the most frequent allelic losses were NF2, l-myc, and p53 (75%, 44%, and 44%, respectively). The average frequency of allelic loss across all tumors was 44% and was higher in tumors that recurred. A combination of previously described high-risk variables (increased patient age and cervical lymph node metastases) with the frequency of allelic loss yielded a high-risk group, in which 6 of 6 patients recurred, and a low-risk group, in which 0 of 5 patients recurred (P = 0.004). Frequency of allelic loss in tumor suppressor genes may provide a useful adjunctive prognostic test in medullary thyroid carcinoma.