Abstract PD02-01: Human Breast Cancer Lymphovascular Tumoral Emboli and Micrometastasis Recapitulate an In Vitro Mammosphere Stem Cell Phenotype

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 that give rise to micrometastases in numerous organs, we wondered whether tumor emboli and micrometastases from actual human cancers also recapitulated a mammosphere stem cell phenotype. Material and Methods: We carried out laser capture microdissection of tumor emboli and lymph node micrometastases in 200 cases of human breast cancer including cases of both infiltrating ductal as well as lobular cancer. These cases included all of the common molecular classes of breast cancer including luminal A, luminal B, luminal C, Her-2/neu positive and triple negative including the basal subtype. The common denominator which was studied in all of these cases was the lymphovascular embolus and lymph node micrometastasis. Results: By both RT-PCR and IHC, lymphovascular emboli and micrometastases 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 than the non-embolic tumoral areas. 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 and micrometastases. These observations held true irrespective of the molecular class of breast cancer from which the embolus was derived and irrespective of the adhesion status (presence or absence of E-cadherin) of the embolus or micrometastasis. Discussion: Our findings indicate that the lymphovascular embolus and micrometastasis 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 and micrometastases to chemotherapy and the decreased disease-free survival and poorer prognosis exhibited by patients with significant lymphovascular emboli and micrometastases. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD02-01.