Lymphovascular Tumor Emboli Recapitulate an In Vitro Mammosphere Stem Cell Phenotype
CE Graham-Lamberts, AL Llewellyn, Y Ye, K Yearsley, SH Barsky. University of Nevada School of Medicine, Reno, NV; The Ohio State University College of Medicine, Columbus, OH; Nevada Cancer Institute, Las Vegas, NV
Background: The existence of stem cells in human cancers has been inferred by clonality experiments and marker studies in vitro and clinical observations in vivo concerning tumor recurrences and emerging drug resistance. We have studied the existence of stem cells in a human model of inflammatory breast cancer, termed MARY-X, a model which forms spheroids which are similar to normal tissue stem cell-derived mammospheres. Comparing MARY-X with common non-IBC breast carcinoma and normal cell lines, we found specific embryonal stem cell markers within the MARY-X spheroids. RT-PCR analyses of MARY-X also revealed the expression of transcriptional determinants essential for the pluripotency and self-renewal of human embryonal stem cells. Since MARY-X spheroids, when injected into mice, form tumors with florid lymphovascular emboli, we wondered whether tumor emboli from actual human cancers also recapitulated a mammosphere stem cell phenotype.
Design: We carried out laser capture microdissection of tumor emboli in 100 cases of human breast cancer including cases of both infiltrating ductal as well as lobular cancer. We also carried out similar dissections of lymphovascular tumor emboli in 50 non-breast cancer cases which included 25 non-small cell lung cancers and 25 pancreatic ductal carcinomas and compared the emboli to areas of non-embolic invasive carcinoma.
Results: By both RT-PCR and IHC, lymphovascular emboli exhibited five-ten fold higher stem cell markers including Stellar, H19, Rex-1, Nestin, CD133 and Aldehyde Dehydrogenase 1 (ALDH1) as well as stem cell transcriptional determinants including OCT4, SOX2, and Nanog. In addition, stem cell signaling pathways specifically involved in self-renewal and pluripotency including Bmi-1, Hedgehog and Notch 3 were activated selectively within the lymphovascular tumor emboli. These observations held true irrespective of the adhesion status (presence or absence of E-cadherin) or organ-specific origin of the embolus.
Conclusions: Our findings indicate that the lymphovascular embolus is not simply a cellular fragment that detaches from the main tumor but rather represents a selection for a stem cell phenotype. This finding may explain the increased resistance of lymphovascular tumor emboli to chemotherapy and the decreased disease-free survival and poorer prognosis exhibited by patients with significant lymphovascular emboli.
Monday, March 22, 2010 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 222, Monday Morning