236 Chapter 16 Abstract Introduction The World Health Organization (WHO) recognizes adenocarcinoma in situ (AIS) for tumors that are up to 3 cm in size. Tumors with the same growth pattern but larger in diameter are considered invasive and classified as lepidic predominant adenocarcinoma. The aim of this study was to examine pulmonary adenocarcinomas larger than 7 cm in diameter to see if any cases fit the criteria of AIS. Materials and Methods In two cases, where initial histological sampling revealed AIS, while on radiology a pneumonia-like pattern in nearly a whole lobe was present, the whole lobe was histologically embedded. In a parallel, an extension was performed on previously reported nationwide retrospective cohort of 683 patients, who had undergone lung surgical resection for pT3N0M0 NSCLC between 2010 and 2013, on a subset of 112 patients with a tumor size larger than 7 cm and adenocarcinoma histology. Further selection of possible non-invasive cases was based on pathology reports and review of H&E slides and additional elastin and cytokeratin 7 stainings. Follow-up of possible non-invasive cases was obtained, and their radiologic was reviewed along with matched controls. Results In two patients the entire lobe was examined, with respectively 130 and 300+ formalin fixed and paraffin embedded tissue blocks. The histological diagnosis supported by additional stainings was AIS, both with a size of 16 cm. In none of the slides criteria for invasion were detected. In the observational study, 7 out of 112 cases were initially identified as possible non-invasive non-mucinous adenocarcinoma based on H&E staining. Subsequent analysis using additional staining techniques revealed that 3 of these cases could be reclassified as non-invasive/AIS. One of the 7 cases was micropapillary, 2 cases were identified as papillary, and 1 case had a lepidic predominant pattern with an invasive acinar component. Radiological imaging indicated that the non-invasive cases exhibited a consolidation pattern, similar to that seen in pneumonia, while the invasive control cases had a primarily solid appearance, a radiologic pattern that was also seen in the papillary adenocarcinoma. Follow-up showed favorable recurrence-free survival in the patients with AIS. Conclusion AIS can be diagnosed in tumors larger than 7cm. The restriction of 3 cm size criterion for AIS in the current World Health classification of pulmonary adenocarcinomas may be reconsidered.
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