The Lymphovascular Embolus of Inflammatory Breast Cancer Expresses a Stem Cell-Like Phenotype

Abstract

Inflammatory breast carcinoma (IBC) is a particularly lethal form of breast cancer characterized by exaggerated lymphovascular invasion, which is a phenotype recapitulated in our human xenograft MARY-X. MARY-X generated spheroids in vitro that resemble the embryonal blastocyst. Because of the resemblance of the spheroids to the embryonal blastocyst and their resistance to traditional chemotherapy/radiotherapy, we hypothesized that the spheroids expressed a stem cell-like phenotype. MARY-X spheroids expressed embryonal stem cell markers including stellar, rex-1, nestin, H19, and potent transcriptional factors, oct-4, nanog, and sox-2, which are associated with stem cell self-renewal and developmental potential. Most importantly, MARY-X spheroids expressed a cancer stem cell profile characterized by CD44 Inflammatory breast cancer (IBC) is an aggressive form of human breast cancer characterized by florid lymphovascular invasion (LVI) and early metastasis.1,2 LVI is considered an important rate-limiting step in the metastatic process and is characterized by the formation of tumor emboli within lymphovascular channels.3,4 These emboli are relatively resistant to radiotherapy and chemotherapy because the tight aggregates of tumor cells exert autocrine and paracrine cytoprotective effects from these therapies by unknown mechanisms. 5,6 These emboli are also efficient at escaping local organ confinement with subsequent distant implantation. They therefore exhibit a strong penchant for both distant metastasis as well as local recurrence and confound attempts at both local as well as systemic control. The tumor emboli bear a strong resemblance to the human embryonal blastocyst, a structure also efficient at escaping local organ confinement with subsequent distant implantation. The IBC phenotype has been successfully recapitulated in a human xenograft model of IBC termed MARY-X.3-7 This model exhibits florid LVI in vivo, which generates tight aggregates of tumor cells (spheroids) in vitro. These spheroids also bear a strong resemblance to the blastocyst. Because the blastocyst is the source of human embryonal stem cells (ESs), cells capable of self renewal, proliferation and differentiation along multiple lineages and because tumor stem cells have been implicated in the properties of local recurrence, distant metastasis, and drug resistance that human cancers exhibit, we hypothesized that the tumor lymphovascular emboli of MARY-X and its derived spheroids might, in fact, express a stem cell-like phenotype reflected by both stem cell markers and stem cell biology. In addition we could test this hypothesis in human cases of IBC and, if confirmed, might explain some of the aggressive behavior of IBC.

Implications of Different Cancer Stem Cell Phenotypes in Breast Cancer

“…In addition, the recent use of CD133 to detect circulating tumor cells in patients with triple-negative breast cancer (71,72) has increased the attention on this marker, emphasizing its role in prognosis in this breast cancer subtype. Expression of CD133 was also recently reported in 22 out of 25 cases of inflammatory breast cancer (13). Taken together, these interesting results indicate the need for more advanced research to understand the role of CD133 in BCSCs.…”

“…Due to the observations that not all BCSC markers are expressed in all breast cancer subtypes, research for different BCSC markers and different combinations of these markers that could be restricted to a specific breast cancer subtype or associated with aggressive forms of this disease is ongoing (12,13). As a consequence, different BCSC phenotypes have been described and characterized, and in the future, other molecules will be reported to have stem cell properties.…”

The lymphovascular embolus of inflammatory breast cancer exhibits a Notch 3 addiction

“…The downstream genes, HES-5 and HEY-2, were noted by expression profiling also to be overexpressed (Po0.0001), suggesting the possibility of Notch signaling. More detailed reverse transcriptase (RT)-PCR, real-time RT-PCR, western blot and immunocytochemical studies looking at Notch 3 (Xiao et al, 2008) and expanding the number of Notch targets confirmed these findings .…”

“…LVI is considered a rate-limiting step in the metastatic process and is characterized by tumor emboli within lymphovascular channels. These emboli are resistant to radiotherapy and chemotherapy (Alpaugh and Barsky, 2002;Alpaugh et al, 2002a, b;Xiao et al, 2008). The IBC phenotype has been successfully recapitulated in a human xenograft model of IBC termed MARY-X (Tomlinson et al, 2001).…”

Early to Intermediate Steps of Tumor Embolic Formation Involve Specific Proteolytic Processing of E-Cadherin Regulated by Rab7

“…Our laboratory has been studying the lymphovascular embolus for a number of years using a unique human xenograft model of inflammatory breast cancer (IBC), MARY-X, a model which spontaneously exhibits florid lymphovascular emboli and widespread metastasis (2). Emerging evidence has suggested that the lymphovascular embolus is not a mere fragment of the main tumoral mass derived from it passively and stochastically but represents an active clonal selection for a stem cell phenotype exhibiting enhanced stem cell signaling and survival pathways (3,4). Only a fraction of MARY-X consists of lymphovascular emboli in vivo and only a fraction of the cells of MARY-X actually form spheroids in vitro.…”