CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4.In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed.A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

Carcinoembryonic antigen (CEA) is a tumor marker for detecting recurrences of adenocarcinomas such as colon cancer. In lung adenocarcinoma, CEA elevation can be found in both serum and malignant pleural effusion. However, CEA elevation in cytologically negative pleural effusion in the presence of adenocarcinoma without pleural infiltration has not been described. We here present the case of an 82-year-old man with incidental early stage adenocarcinoma of the right upper lobe showing CEA elevation in pleural fluid and serum despite negative cytological findings. Due to limited lung reserve the tumor was removed by wide wedge resection, but the visceral pleura was not affected and infiltration of the parietal pleura was ruled out by pleural biopsies. Serum and pleural CEA levels declined postoperatively as measured at 1 and 2 months follow-up. This case shows CEA elevation in serum and pleural fluid in early stage lung adenocarcinoma with negative cytology and no sign of pleural infiltration. Previous research revealed that CEA level in pleural effusion correlates to serum CEA and is significantly higher in adenocarcinoma of the lung than in other lung cancer entities. Firstly, this case suggests that determination of CEA levels can increase the diagnostic sensitivity in cases with cytologically negative pleural effusion suspicious of malignant origin and secondly, it contributes valuable information to the decision whether follow-up of pulmonary nodules or continuative diagnostics such as video-assisted thoracoscopic surgery (VATS) wedge resection is indicated.

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Bronchial sleeve resections are performed in lung malignancies involving major airways. Key to smooth healing of the anastomosis is an optimal vascularization. Many techniques have been proposed for anastomosis protection and revascularization; the preservation of the bronchial artery has not been considered, however. We present a modification of a partial sleeve left lower lobe resection in which we preserve the left upper bronchus artery by leaving the dorsal wall between the main and the left upper lobe bronchus intact, thus maintaining a physiologic vascularization to the anastomosis.