Immunohistochemical algorithm for differentiation of lung adenocarcinoma and squamous cell carcinoma based on large series of whole-tissue sections with validation in small specimens

Abstract

Immunohistochemistry is increasingly utilized to differentiate lung adenocarcinoma and squamous cell carcinoma. However, detailed analysis of coexpression profiles of commonly used markers in large series of whole-tissue sections is lacking. Furthermore, the optimal diagnostic algorithm, particularly the minimalmarker combination, is not firmly established. We therefore studied whole-tissue sections of resected adenocarcinoma and squamous cell carcinoma (n ¼ 315) with markers commonly used to identify adenocarcinoma (TTF-1) and squamous cell carcinoma (p63, CK5/6, 34bE12), and prospectively validated the devised algorithm in morphologically unclassifiable small biopsy/cytology specimens (n ¼ 38). Analysis of whole-tissue sections showed that squamous cell carcinoma had a highly consistent immunoprofile (TTF-1-negative and p63/CK5/6/34bE12-diffuse) with only rare variation. In contrast, adenocarcinoma showed significant immunoheterogenetity for all 'squamous markers' (p63 (32%), CK5/6 (18%), 34bE12 (82%)) and TTF-1 (89%). As a single marker, only diffuse TTF-1 was specific for adenocarcinoma whereas none of the 'squamous markers,' even if diffuse, were entirely specific for squamous cell carcinoma. In contrast, coexpression profiles of TTF-1/p63 had only minimal overlap between adenocarcinoma and squamous cell carcinoma, and there was no overlap if CK5/6 was added as a third marker. An algorithm was devised in which TTF-1/p63 were used as the first-line panel, and CK5/6 was added for rare indeterminate cases. Prospective validation of this algorithm in small specimens showed 100% accuracy of adenocarcinoma vs squamous cell carcinoma prediction as determined by subsequent resection. In conclusion, although reactivity for 'squamous markers' is common in lung adenocarcinoma, a two-marker panel of TTF-1/p63 is sufficient for subtyping of the majority of tumors as adenocarcinomas vs squamous cell carcinoma, and addition of CK5/6 is needed in only a small subset of cases. This simple algorithm achieves excellent accuracy in small specimens while conserving the tissue for potential predictive marker testing, which is now an essential consideration in advanced lung cancer specimens. Modern Pathology (2011Pathology ( ) 24, 1348Pathology ( -1359 doi:10.1038/modpathol.2011; published online 27 May 2011Keywords: adenocarcinoma; CK5/6; p63; squamous cell carcinoma; TTF-1; 34bE12Adenocarcinoma and squamous cell carcinoma are the two major subtypes of non-small cell lung carcinoma. Until recently, therapeutic approaches to non-small cell lung carcinoma were largely guided by tumor stage, and there was no difference in treatment for adenocarcinoma vs squamous cell carcinoma. This monolithic approach to non-small cell lung carcinoma has dramatically changed in the last few years as a result of three major advances in thoracic medical oncology for advanced disease. These include (1) EGFR-targeted therapies, erlotinib

Utility of small biopsies for diagnosis of lung nodules: doing more with less

“…However, recent immunohistochemical studies that have focused on poorly differentiated non-small cell carcinomas in small biopsies or cytology specimens with resected tumors as the gold standard have shown that some markers, especially when used in combination, are indeed useful and accurate in subclassifying poorly differentiated non-small cell lung carcinomas. [5][6][7][8] As subclassification using these markers shows excellent correlation with the gold standard H&E-based diagnosis on resected tumors, immunohistochemistry has become accepted as a reliable technique for subclassification when diagnostic features on H&E morphology are absent in a small biopsy. To summarize the current state of non-small cell lung carcinoma subclassification, H&E-based criteria remain the gold standard for subclassifying resected tumors.…”

“…Similarly, although p63 is more sensitive for squamous cell carcinomas than CK5/6, the latter is useful when p63 staining is focal, weak or equivocal. 7 In samples for which cellularity is very low, it has been suggested that a more limited panel composed of TTF-1 and p63 can be used in most cases to conserve the tissue in the event that it is required for molecular studies. 7 Similar concerns have been cited by a consensus panel in recommending that the panel be limited to TTF-1 and p63, with or without a mucin stain.…”

“…7 In samples for which cellularity is very low, it has been suggested that a more limited panel composed of TTF-1 and p63 can be used in most cases to conserve the tissue in the event that it is required for molecular studies. 7 Similar concerns have been cited by a consensus panel in recommending that the panel be limited to TTF-1 and p63, with or without a mucin stain. 11 To date, however, there is no evidence that using one or two additional sections (ie, a 4-marker panel vs a 3-or a 2-marker panel) for immunohistochemistry diminishes the yield of subsequent molecular studies.…”

“…This pattern of staining is fairly common in poorly differentiated adenocarcinomas and should not be misinterpreted as evidence of adenosquamous carcinoma. 5,7 In cases in which TTF-1 staining is not significantly different from p63 staining, positivity for napsin A can be very helpful to support a diagnosis of poorly differentiated adenocarcinoma ( Figure 7). Diffuse positivity for both TTF-1 and p63 in the same population of cells is distinctly uncommon, but should also be interpreted as poorly differentiated adenocarcinoma, especially if napsin A is also positive.…”

Cross-cancer profiling of molecular alterations within the human autophagy interaction network

“…71 However, LUAD and LUSC also differ at the molecular level. For example, activating mutations in tyrosine kinase signaling pathway genes (e.g., EGFR, ALK, RET, ERBB2) are common in LUAD, while NFE2L2 mutations are a distinguishing feature of LUSC.…”