Prognosis of young women’s breast cancer is influenced by reproductive history. Women diagnosed within five years postpartum have worse prognosis than nulliparous women or women diagnosed during pregnancy. Here we describe a mouse model of postpartum breast cancer that identifies mammary gland involution as a driving force of tumor progression. In this model, human breast cancer cells exposed to the involuting mammary microenvironment form large tumors characterized by abundant fibrillar collagen, high COX-2 expression, and an invasive phenotype. In culture, tumor cells are invasive in a fibrillar collagen and COX-2-dependent manner. In the involuting mammary gland, inhibition of COX-2 reduces the collagen fibrillogenesis associated with involution, as well as tumor growth and tumor cell infiltration to the lung. These data support further research to determine whether women at high-risk for postpartum breast cancer would benefit from treatment with NSAIDs during postpartum involution.

Recent pregnancy correlates with decreased survival for breast cancer patients compared with non-pregnancy-associated breast cancer. We hypothesize that postpartum mammary involution induces metastasis through wound-healing programs known to promote cancer. It is unknown whether alternatively activated M2 macrophages , immune cells important in woundhealing and experimental tumorigenesis that also predict poor prognosis for breast cancer patients, are recruited to the normal involuting gland. Macrophage markers CD68 , CSF-1R , and F4/80 were examined across the pregnancy and involution cycle in rodent and human mammary tissues. Quantitative immunohistochemistry revealed up to an eightfold increase in macrophage number during involution , which returned to nulliparous levels with full regression. The involution macrophages exhibit an M2 phenotype as determined by high arginase-1 and low inducible nitric oxide synthase staining in rodent tissue , and by mannose receptor expression in human breast tissue. M2 cytokines IL-4 and IL-13 also peaked during involution. Extracellular matrix (ECM) isolated from involuting rat mammary glands was chemotactic for macrophages compared with nulliparous mammary ECM. Although it is recognized that full-term pregnancy at an early age reduces the lifetime risk of developing breast cancer, women of all ages have a transient increase in breast cancer risk with a recent pregnancy.1-4 Breast cancers diagnosed up to five years out from a completed pregnancy have been referred to as pregnancy-associated or PABC. 5,6 Several studies have shown that PABC frequently metastasizes, resulting in poor prognosis for the patient.6 -8 Epidemiological data identify women whose breast cancer is diagnosed postpartum, rather than during pregnancy, as having the worst outcomes.7-14 Further, when breast cancer patients were matched for known prognostic indicators, the postpartum window proved to be an independent factor for metastasis, whereas a diagnosis during pregnancy did not. 11,14,15 We have proposed the involution-hypothesis to account for the high metastatic oc-

Previous studies report conflicting data on outcomes of pregnancy-associated breast cancer (PABC). Our aim was to examine the effect of a postpartum diagnosis on maternal prognosis in a young women’s breast cancer cohort. We conducted a retrospective cohort study of women age ≤45 years, diagnosed with breast cancer (n = 619) during 1981–2011 at the University of Colorado Hospital and The Shaw Cancer Center in Edwards, CO. Breast cancer cases were grouped according to time between giving birth and diagnosis: nulliparous (n = 125), pregnant (n = 24), < 5 years postpartum (n = 136), >5—<10 postpartum (n = 130), and ≥10 years postpartum (n = 147), to examine the clinicopathologic features and the risk of distance recurrence and death. Cases diagnosed after pregnancy, but within five-years postpartum, had an approximate three fold increased risk of distant recurrence (HR 2.80, 95 % CI: 1.12–6.57) and death (HR 2.65, 95 % CI: 1.09–6.42) compared to nulliparous cases. Postpartum cases diagnosed within five years of last childbirth demonstrated a higher five-year distant recurrence probability (31.1 %) and a markedly lower five-year overall survival probability (65.8 %) compared to nulliparous cases (14.8 and 98.0 %, respectively). A diagnosis of breast cancer during the first five-years postpartum confers poorer maternal prognoses after adjustment for biologic subtype, stage, and year of diagnosis. We propose that the definition of PABC should include cases diagnosed up to at least five-years postpartum to better delineate the increased risk imparted by a postpartum diagnosis. Based on emerging preclinical and epidemiologic data, we propose that pregnant and postpartum cases be researched as distinct subsets of PABC to clarify the risk imparted by pregnancy and the events subsequent to pregnancy, such as breast involution, on breast cancer. Further, we highlight the importance of postpartum breast cancer as an area for further research to reduce the increased metastatic potential and mortality of PABC.Electronic supplementary materialThe online version of this article (doi:10.1007/s10549-013-2437-x) contains supplementary material, which is available to authorized users.

Women of childbearing age experience an increased breast cancer risk associated with a completed pregnancy. For younger women, this increase in breast cancer risk is transient and within a decade after parturition a cross over effect results in an ultimate protective benefit. The post-partum peak of increased risk is greater in women with advanced maternal age. Further, their lifetime risk for developing breast cancer remains elevated for many years, with the cross over to protection occurring decades later or not at all. Breast cancers diagnosed during pregnancy and within a number of years post-partum are termed pregnancy-associated or PABC. Contrary to popular belief, PABC is not a rare disease and could affect up to 40,000 women in 2009. The collision between pregnancy and breast cancer puts women in a fear-invoking paradox of their own health, their pregnancy, and the outcomes for both. We propose two distinct subtypes of PABC: breast cancer diagnosed during pregnancy and breast cancer diagnosed post-partum. This distinction is important because emerging epidemiologic data highlights worsened outcomes specific to post-partum cases. We reported that post-partum breast involution may be responsible for the increased metastatic potential of post-partum PABC. Increased awareness and detection, rationally aggressive treatment, and enhanced understanding of the mechanisms are imperative steps toward improving the prognosis for PABC. If we determine the mechanisms by which involution promotes metastasis of PABC, the post-partum period can be a window of opportunity for intervention strategies. The interactions between pregnancy and breast cancer are complex and variable. More often than is frequently realized, these interactions are negative with regard to the resultant outcomes. The influence of pregnancy on the risk of developing breast cancer is dependent on maternal features, including age, family history, lactation postpartum, and overall parity. The risk for future breast cancer after a pregnancy follows a pattern curve of increased then decreased risk over time, with the zenith and subsequent

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Chimeric poliovirus RNAs, possessing the 5 nontranslated region (NTR) of hepatitis C virus in place of the 5 NTR of poliovirus, were used to examine the role of the poliovirus 5 NTR in viral replication. The chimeric viral RNAs were incubated in cell-free reaction mixtures capable of supporting the sequential translation and replication of poliovirus RNA. Using preinitiation RNA replication complexes formed in these reactions, we demonstrated that the 3 NTR of poliovirus RNA was insufficient, by itself, to recruit the viral replication proteins required for negative-strand RNA synthesis. The 5-terminal cloverleaf of poliovirus RNA was required in cis to form functional preinitiation RNA replication complexes capable of uridylylating VPg and initiating the synthesis of negative-strand RNA. These results are consistent with a model in which the 5-terminal cloverleaf and 3 NTRs of poliovirus RNA interact via temporally dynamic ribonucleoprotein complexes to coordinately mediate and regulate the sequential translation and replication of poliovirus RNA.The single-stranded positive-sense RNA genome of poliovirus functions sequentially as an mRNA for viral protein synthesis and then as a template for viral negative-strand RNA synthesis (33). Cytoplasmic extracts from HeLa cells support the sequential translation and replication of poliovirus RNA (5, 31). In the presence of 2 mM guanidine HCl, cell-free translation-replication reactions support the translation of viral RNA and the accumulation of viral preinitiation RNA replication complexes (4, 6). Guanidine HCl reversibly blocks the initiation of negative-strand RNA synthesis by interfering with the function of viral protein 2CATPase (3,38,40). When preinitiation RNA replication complexes are resuspended in reaction mixtures in the absence of guanidine HCl, the preinitiation RNA replication complexes synchronously initiate the synthesis of viral negative-strand RNA (6). Ribosomes translating the viral mRNA within preinitiation RNA replication complexes prevent the synthesis of negative-strand RNA (8,15). Thus, the conversion of viral ribonucleoprotein complexes into preinitiation RNA replication complexes is an important temporally regulated event in the replication of poliovirus RNA.Contemporary models of eukaryotic mRNA translation suggest that the 5Ј and 3Ј nontranslated regions (NTRs) of mRNAs communicate via RNA binding proteins bound to both termini of the mRNA (14,19,42). In particular, poly(A) binding protein bound to 3Ј-terminal poly(A) interacts with eukaryotic initiation factors eIF4G I and II anchored to the 5Ј NTR of mRNA, bringing the 5Ј and 3Ј NTRs into proximity (49). During the course of a poliovirus infection, viral protein 2APro mediates the cleavage of eIF4G I and II and poly(A) binding proteins (11,18,23,24). This leads to the shutoff of cap-dependent host protein synthesis and precludes the ability of eIF4G I and II and poly(A) binding protein to form proteinprotein bridges between the 5Ј and 3Ј termini of mRNAs, including poliovirus RNA. Therefo...

The limitations of cancer cell lines have led to the development of direct patient derived xenograft (PDX) models. However, the interplay between the implanted human cancer cells and recruited mouse stromal and immune cells alters the tumor microenvironment and limits the value of these models. To overcome these constraints, we have developed a technique to expand human hematopoietic stem and progenitor cells (HSPCs) and use them to reconstitute the radiation-depleted bone marrow of a NOD/SCID/IL2rg−/− (NSG) mouse on which a patient’s tumor is then transplanted (XactMice). The human HSPCs produce immune cells that home into the tumor and help replicate its natural microenvironment. Despite previous passage on nude mice, the expression of epithelial, stromal, and immune genes in XactMice tumors aligns more closely to that of the patient tumor than to those grown in non-humanized mice – an effect partially facilitated by human cytokines expressed by both the HSPC progeny and the tumor cells. The human immune and stromal cells produced in the XactMice can help recapitulate the microenvironment of an implanted xenograft, reverse the initial genetic drift seen after passage on non-humanized mice, and provide a more accurate tumor model to guide patient treatment.

Postpartum mammary gland involution is a tissue remodeling event that occurs in all mammals in the absence of nursing or after weaning to return the gland to the pre-pregnant state. The tissue microenvironment created by involution has proven to be tumor promotional. Here we report that the GPI-linked protein semaphorin 7a (SEMA7A) is expressed on mammary epithelial cells during involution and use preclinical models to demonstrate that tumors induced during involution express high levels of SEMA7A. Overexpression of SEMA7A promoted the presence of myeloid-derived podoplanin (PDPN)-expressing cells in the tumor microenvironment and during involution. SEMA7A drove the expression of PDPN in macrophages, which led to integrin- and PDPN-dependent motility and adherence to lymphatic endothelial cells to promote lymphangiogenesis. In support of this mechanism, mammary tissue from SEMA7A-knockout mice exhibited decreased myeloid-derived PDPN-expressing cells, PDPN-expressing endothelial cells, and lymphatic vessel density. Furthermore, co-expression of SEMA7A, PDPN, and macrophage marker CD68 predicted for decreased distant metastasis-free survival in a cohort of over 600 cases of breast cancer as well as in ovarian, lung, and gastric cancers. Together our results indicate that SEMA7A may orchestrate macrophage-mediated lymphatic vessel remodeling, which in turn drives metastasis in breast cancer