Abstract 11: Prophylactic use of tamoxifen could reduce the risk of breast cancer in women who do not breast feed postpartum

Background: Triple negative breast cancer (TNBC) is associated with poor survival, particularly affecting African American women (AAW). Epidemiological studies indicate prolonged breast feeding reduces breast cancer (BC) risk, including TNBC. AAW have significantly lower rates of breast feeding compared to Caucasian women. To understand this link we developed a mouse model mimicking abrupt (AI) and gradual involution (GI). AI led to increased estrogen signaling, cell proliferation and chronic inflammation, which was followed by hyperplasia and squamous metaplasia in mammary glands1. There was an increase in the luminal progenitor (LP) cell population, the cells of origin of TNBC, and a decrease in mature luminal (ML) cells in AI glands. In this study, we sought to determine if blocking estrogen signaling with tamoxifen (TAM) could revert the negative effects of AI, and if so, could be a prophylactic option to reduce BC risk in women who do not breast feed.

Methods: Uniparous FVB/N mice (~8 weeks) were allowed to nurse six pups per dam at partum. To induce AI, all pups were removed on postpartum (PP) day 7 (d7). For TAM treatment, 5mg sustained release TAM citrate pellet or placebo was implanted in the subscapular region on PP d8. Mammary glands were harvested on PP d28 and d120. FFPE sections were used for histology and immunohistochemistry. Single cell suspensions were analyzed for mammary epithelial subpopulations using Fluorescence Activated Cell Sorting. Affymetrix and qPCR were used for gene expression analysis. Mass cytometry was performed on mammary glands harvested at PP d120.

Results: TAM treatment for 21 days completely abrogated hyperplastic and metaplastic changes in AI glands harvested on d120. Treatment initiation on PP d8, d15 and d35 had the same effect. TAM treatment reduced the cell proliferation and collagen deposition in AI glands. De-enrichment of estrogen signaling pathways and decrease in Elf5 expression, a luminal progenitor marker, were observed upon TAM treatment in d28 glands. Mass cytometry revealed a marked reduction in LP population and a significant increase in ML population in TAM treated AI glands on d120, restoring to the levels in age matched virgin mice. Significant increases in progenitor-like markers TSPAN8, Ly6D, CD200 and decreases in CD49f and CD47 expression in LP cells were observed, indicating return to a normal uniparous LP state. Expression of Ly-6D in ML cells, a ML cell marker, was also rescued upon TAM treatment.

Conclusion: Using our mouse model of AI and GI, we show that suppression of estrogen signaling after initiation of AI offered marked protection against precancerous changes. TAM restored the balance of epithelial lineages and normalized the LP and basal cells in AI glands to the post-involution phenotype. Our data provide a rationale for considering short-term TAM treatment for women who do not breastfeed to reduce risk of BC. 1. Basree et.al. PMID 31315645

Citation Format: Bhuvaneswari Ramaswamy, Neelam Shinde, Gary K. Gray, Resham Mawalkar, Allen Zhang, Mustafa Basree, Xiaoli Zhang, Ramesh Ganju, Gina M. Sizemore, Joan S. Brugge, Sarmila Majumder. Prophylactic use of tamoxifen could reduce the risk of breast cancer in women who do not breast feed postpartum [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 11.

Abstract P5-01-08: Mechanistic differences between abrupt and gradual involution of mouse mammary gland

Objective: Epidemiological studies indicate a direct relation between length of breast feeding and protection against risk of triple negative breast cancer (TNBC), an aggressive subtype. While prolonged breastfeeding allows gradual involution (GI) of the breast, short-term or no breast feeding leads to abrupt involution (AI). We modelled AI and GI of breast in mice, and showed that mice subjected to GI have better protection from tissue remodeling associated injuries in the mammary gland. Our data revealed late development of ductal hyperplasia aided by pro-tumorigenic microenvironment in the AI glands1. Detailed mechanism of mammary gland involution immediately following cessation of lactation has been studied in the past, but only in the AI setting, that is after abrupt removal of pups at the peak of lactation2,3. The goal of this study is to conduct stepwise comparison of the mechanism of GI vs. AI early on to understand the protective effect of GI against breast cancer risk.Methods: Wild-type FVB mice were used in all our studies. Females were mated at 8 weeks of age and uniparous mice were allowed to nurse (6 pups/dam) for 7 days. Females were then assigned randomly to AI or GI cohort. All pups were removed from the AI dams on postnatal day7 (PND7). Three pups each were removed from GI dams on day28 and 31. Mammary glands were harvested intermittently between PND7 and PND35. H&E stained sections were used for histological studies. Unstained FFPE sections were used for immunohistochemistry and TUNEL assay. Total RNA and protein from whole mammary gland was used for qPCR and western blot respectively. Results: GI glands transitioned from fully active lactating to near involuted glands over a period of 8 days (PND17- PND25), while for AI glands it took < 4 days (PND8.5-PND12). The shrinkage and flattening of tall epithelia and loss of acini was gradual in GI glands as opposed to rapid breakdown of acini and adipocyte repopulation in AI gland. Apoptotic cell count peaked on PND11 (5%) in AI vs. PND25 (3%) in GI glands. The pStat3Y705+ cells were highest on PND8.5 (25%) in AI vs. on PND25 (11%) in GI glands. Macrophage infiltration (F4/80+) peaked on PND11 (35%) and remained elevated at ~24% till PND25, while in GI glands increase was gradual from PND17 through PND25 (27%). Expression of key genes identified in AI mice2,3 have markedly different expression pattern in GI mice (Table). While some peaked at a later time point in GI vs. AI coinciding with maximum cell death, expression of some are significantly low or undetectable in GI glands at both RNA and protein level. Conclusions: We show for the first time that kinetics of cell death, adipocyte repopulation, immune cell infiltration and inflammatory state of glands undergoing abrupt vs. gradual involution are markedly different. Several genes known to play a key role during AI are either not expressed or barely detectable in the GI glands at any time point during involution. These data suggests that not only the kinetics, but mechanism of GI and AI are not identical. We conclude that orchestrated cell death in GI protects from drastic lysosomal, and immune cell activities that predisposes mammary glands to higher risk of neoplastic changes.Significance: Epidemiological data highlights the benefits of prolonged breastfeeding in protecting against breast cancer, particularly, TNBC, an aggressive subtype prevalent in the African American women. Our study highlights the mechanism underlying the benefits of gradual involution of breast.

GeneFold Change compared to PND7 (GI vs. AI) Peaked on (GI vs. AI)Stat34.0 vs. 5.9PND25 vs. PND8.5Ctsb2.8 vs. 3.4PND25 vs. PND8.5CD143.4 vs. 20PND25 vs. PND8.5Orm11.7 vs. 10PND25 vs. PND12Lrg130 vs. 216PND25 vs. PND12MMP215.8 vs. 27PND25 vs. PND12Chi3L11350 vs. 572, 859PND28 vs. PND11, 28Cebpδnone vs. 4.4None vs. PND8.5CtsLnone vs. 5.7None vs. PND8.5Orm2none vs. 370None vs. PND12Slpinone vs. 92None vs. PND8.5

Citation Format: Bhuvaneswari Ramaswamy, Neelam Shinde, Morgan Bauer, Maria Cuitino, Saba Mehra, Resham Mawalkar, Mustafa Basree, Allen Zhang, Kirti Kaul, Xiaoli Zhang, Ramesh Ganju, Sarmila Majumder. Mechanistic differences between abrupt and gradual involution of mouse mammary gland [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-01-08.

Comprehensive Review of Molecular Mechanisms and Clinical Features of Invasive Lobular Cancer

Invasive lobular carcinoma (ILC) accounts for 10% to 15% of breast cancers in the United States, 80% of which are estrogen receptor (ER)-positive, with an unusual metastatic pattern of spread to sites such as the serosa, meninges, and ovaries, among others. Lobular cancer presents significant challenges in detection and clinical management given its multifocality and multicentricity at presentation. Despite the unique features of ILC, it is often lumped with hormone receptor-positive invasive ductal cancers (IDC); consequently, ILC screening, treatment, and follow-up strategies are largely based on data from IDC. Despite both being treated as ER-positive breast cancer, querying the Cancer Genome Atlas database shows distinctive molecular aberrations in ILC compared with IDC, such as E-cadherin loss (66% vs. 3%), FOXA1 mutations (7% vs. 2%), and GATA3 mutations (5% vs. 20%). Moreover, compared with patients with IDC, patients with ILC are less likely to undergo breast-conserving surgery, with lower rates of complete response following therapy as these tumors are less chemosensitive. Taken together, this suggests that ILC is biologically distinct, which may influence tumorigenesis and therapeutic strategies. Long-term survival and clinical outcomes in patients with ILC are worse than in stage- and grade-matched patients with IDC; therefore, nuanced criteria are needed to better define treatment goals and protocols tailored to ILC's unique biology. This comprehensive review highlights the histologic and clinicopathologic features that distinguish ILC from IDC, with an in-depth discussion of ILC's molecular alterations and biomarkers, clinical trials and treatment strategies, and future targets for therapy. IMPLICATIONS FOR PRACTICE: The majority of invasive lobular breast cancers (ILCs) are hormone receptor (HR)-positive and low grade. Clinically, ILC is treated similar to HR-positive invasive ductal cancer (IDC). However, ILC differs distinctly from IDC in its clinicopathologic characteristics and molecular alterations. ILC also differs in response to systemic therapy, with studies showing ILC as less sensitive to chemotherapy. Patients with ILC have worse clinical outcomes with late recurrences. Despite these differences, clinical trials treat HR-positive breast cancers as a single disease, and there is an unmet need for studies addressing the unique challenges faced by patients diagnosed with ILC.

Abstract PS17-28: Abrupt involution of lactating mammary gland induces metabolic reprogramming conducive to pro-tumorigenic changes

Background: Epidemiological studies indicate that prolonged breast feeding reduces the risk of triple negative breast cancer (TNBC), which carries the worst prognosis. Prolonged breastfeeding allows gradual involution (GI) of the breast while lack of or short-term breast feeding leads to abrupt involution (AI). We developed a novel murine model mimicking AI and GI of breast, and found that GI offers better protection to mammary glands from tissue remodeling associated injuries. Our data showed that AI leads to the development of pro-tumorigenic microenvironment and ductal hyperplasia1. Tissue remodeling involves orchestrated cell death and repopulation, and is closely associated with metabolic reprogramming from mitochondrial oxidative phosphorylation (OXPHOS) to glycolysis. Such metabolic alterations can contribute to cellular changes aiding malignant transformation2. We used our murine model to evaluate whether AI affects cellular metabolism differentially when compared to GI. Methods: Wild-type mice of FVB background were used in all our experiments. Twelve to fourteen week old uniparous mice were allowed to nurse (6 pups/dam) for 7 days postpartum. All pups were removed on day7 postpartum from the dams in AI cohort and three each on day28 and day31 from dams in GI cohort. Whole mammary glands and sorted luminal progenitor (LP) cells harvested on postpartum day28 were subjected to Affymetrix microarray analysis. Gene Set Enrichment Analysis (GSEA) was used to compute pathway enrichments in AI vs. GI glands. Differentially expressed genes were validated using qRT-PCR. Mammary glands harvested on day28 postpartum were subjected to mass spectrometry based untargeted metabolic profiling using Agilent QTOF. Raw data were analyzed using XCMS to assess key metabolic networks altered in AI vs GI glands. Targeted analysis for lactate, pyruvate, succinate and palmitic acid were performed using C13 labelled internal standards to compare OXPHOS vs glycolysis reliance in the AI and GI glands. Results: We observed enrichment of mitochondrial OXPHOS pathway, fatty acid metabolism and Myc target genes in both whole mammary gland and LP cells of AI vs. GI mice. Adipogenesis and hypoxia related genes were enriched in AI-glands. We observed significant upregulation of genes involved in glucose transport and fatty acid synthesis in AI glands, namely, Glut-5, Cidea, Acss2, Acsm3, Acly, Atp6v0d2, Acot11, and Elvol3. Several factors indicating a higher reliance on OXPHOS vs glycolysis, such as, Ppar-γ, Pgc1α, Cpt-2, Srebp1c and Chrebp were upregulated in AI glands. Upregulation of Cpt-2 and Srebp1c in the AI glands indicate higher flux through fatty acid oxidation and reliance on cholesterol synthesis. Metabolomic profiling revealed significant alteration in L-carnitine, GMP and XMP in AI glands which reflect mitochondrial fatty acid transport and nucleotide biosynthesis via guanine-guanosine salvage pathway. Pyruvate and lactate associated with glycolysis were increased in GI vs. AI glands. Conclusion: We show for the first time that in the abruptly involuting (AI) mammary glands following short-term breast feeding, there is a significant shift in the metabolic pathways towards mitochondrial OXPHOS and fatty acid oxidation compared to GI glands. Studies are underway to determine the effect of this metabolic shift on cellular transformation and tumorigenesis and the potential to target these pathways to reverse the detrimental effects of AI. 1. Basree MM, Shinde N, Koivisto C, et al. Breast Cancer Res. 2019; 21(1):80. 2. Ward PS, Thompson CB. Cancer Cell. 2012; 21(3):297.

Citation Format: Neelam Shinde, Kirti Kaul, Allen Zhang, Saba Mehra, Resham Mawalkar, Hee Kyung Kim, Ramesh Ganju, Sarmila Majumder, Bhuvaneswari Ramaswamy. Abrupt involution of lactating mammary gland induces metabolic reprogramming conducive to pro-tumorigenic changes [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-28.

Abstract P5-07-11: Mammary gland specific Stat3 deletion during involution results in distinct histological changes and higher collagen deposition

Rationale: African American women (AAW) have a higher incidence of triple negative breast cancer (TNBC), and higher mortality from breast cancer when compared to Caucasian women (CW). Epidemiological studies have shown that lack, or short duration, of breast-feeding, a more common practice among AAW than CW, may be one of the factors that increase the risk of TNBC. The pregnancy-lactation-involution cycle is a dynamic process where upon pregnancy, breast undergoes extensive proliferation and differentiation for milk production followed by apoptosis as it involutes to near pre-pregnant state. Prolonged breastfeeding results in gradual involution (GI) whereas no or short duration of breastfeeding leads to forced and abrupt involution (AI) of breast. We modeled GI and AI in wild-type FVB/N mice and reported that mammary glands of abruptly involuted mice had expansion of luminal progenitor (LP) cells over time and hyperplastic precancerous changes within 120 days postpartum1. In addition, there was increased Stat3 (Signal Transducer and Activator of Transcription 3) activation (pStat3Y705) in AI glands. Persistent Stat3 activation is linked to tumor cell proliferation, survival, invasion, and tumor-promoting inflammation2. In mice, Stat3 is required for the initiation and acute phase response during mammary gland involution and is crucial for the proliferation of LP cells3-5. We hypothesized that Stat3 activation plays a key role in the development of hyperplasia and fibrosis observed following AI.Methods: We bred Stat3Fl/Flmice with MMTV-Cre mice to induce mammary epithelial specific deletion of Stat3. Experimental (MMTV-Cre+;Stat3Fl/Fl) and control females (Stat3Fl/Fl) were bred once at 8 weeks of age and litter sizes were normalized to 6pups/dam within 24 hours of partum. With day of partum as day0, all 6 pups were removed on day7 and AI was initiated. Mammary glands were harvested on postpartum day28, day56, and day120. Florescence activated cell sorting (FACS) was performed to determine distribution of mammary epithelial subpopulations. Histological effects of Stat3 deletion on mammary gland involution was assessed via staining using haematoxylin and eosin (H&E), Masson’s Trichrome and immunostaining using anti-Ki67 and anti-Stat3 antibodies. Results: Stat3 deletion failed to abrogate the hyperplasia and collagen deposition we initially observed in our AI mice with intact Stat3 as determined by H&E and Trichrome stains. In addition, collagen deposition was further increased following Stat3 deletion, when compared to control cohort. FACS analysis demonstrated that Stat3 deletion resulted in reduction of LP cell population only at early timepoint (day28) but this population rebounded in glands by later timepoints. Stat3 deletion temporarily increased cell proliferation by Ki-67 staining at day28 and 56, with no difference observed between controls at day120. Conclusion: This is the first study showing results of mammary epithelial specific Stat3 deletion on long-term effect of AI. Contrary to our hypothesis, Stat3 deletion did not reduce the hyperplastic changes we observed following abrupt involution of mammary glands. Our findings indicate that Stat3 signaling may limit collagen formation within the mammary gland during abrupt involution. Stat3 is important for the maintenance of LP cells at early timepoints. Further studies are underway to determine the critical downstream events following Stat3 activation that limits long-term effects of abrupt involution. 1. Basree et. al. 2019, in press, Breast Cancer Research 2. Yu et. al. 2014 (PMID: 25342631) 3. Chapman et. al. 1999 (PMID: 10521404) 4. Hughes et. al. 2012 (PMID: 22081431)5. Staniszewska et. al. 2012 (PMID: 23285109)

Citation Format: Allen Zhang, Neelam Shinde, Christopher S Koivisto, Mustafa M Basree, Resham S Mawalkar, Hee K Kim, Gustavo Leone, Sarmila Majumder, Bhuvaneswari Ramaswamy. Mammary gland specific Stat3 deletion during involution results in distinct histological changes and higher collagen deposition [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-07-11.

Abrupt involution induces inflammation, estrogenic signaling, and hyperplasia linking lack of breastfeeding with increased risk of breast cancer

Background

A large collaborative analysis of data from 47 epidemiological studies concluded that longer duration of breastfeeding reduces the risk of developing breast cancer. Despite the strong epidemiological evidence, the molecular mechanisms linking prolonged breastfeeding to decreased risk of breast cancer remain poorly understood.

Methods

We modeled two types of breastfeeding behaviors in wild type FVB/N mice: (1) normal or gradual involution of breast tissue following prolonged breastfeeding and (2) forced or abrupt involution following short-term breastfeeding. To accomplish this, pups were gradually weaned between 28 and 31 days (gradual involution) or abruptly at 7 days postpartum (abrupt involution). Mammary glands were examined for histological changes, proliferation, and inflammatory markers by immunohistochemistry. Fluorescence-activated cell sorting was used to quantify mammary epithelial subpopulations. Gene set enrichment analysis was used to analyze gene expression data from mouse mammary luminal progenitor cells. Similar analysis was done using gene expression data generated from human breast samples obtained from parous women enrolled on a tissue collection study, OSU-2011C0094, and were undergoing reduction mammoplasty without history of breast cancer.

Results

Mammary glands from mice that underwent abrupt involution exhibited denser stroma, altered collagen composition, higher inflammation and proliferation, increased estrogen receptor α and progesterone receptor expression compared to those that underwent gradual involution. Importantly, when aged to 4 months postpartum, mice that were in the abrupt involution cohort developed ductal hyperplasia and squamous metaplasia. Abrupt involution also resulted in a significant expansion of the luminal progenitor cell compartment associated with enrichment of Notch and estrogen signaling pathway genes. Breast tissues obtained from healthy women who breastfed for < 6 months vs ≥ 6 months showed significant enrichment of Notch signaling pathway genes, along with a trend for enrichment for luminal progenitor gene signature similar to what is observed in BRCA1 mutation carriers and basal-like breast tumors.

Conclusions

We report here for the first time that forced or abrupt involution of the mammary glands following pregnancy and lack of breastfeeding results in expansion of luminal progenitor cells, higher inflammation, proliferation, and ductal hyperplasia, a known risk factor for developing breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1163-7) contains supplementary material, which is available to authorized users.

Two Distinct E2F Transcriptional Modules Drive Cell Cycles and Differentiation

Orchestrating cell-cycle-dependent mRNA oscillations is critical to cell proliferation in multicellular organisms. Even though our understanding of cell-cycle-regulated transcription has improved significantly over the last three decades, the mechanisms remain untested in vivo. Unbiased transcriptomic profiling of G0, G1-S, and S-G2-M sorted cells from FUCCI mouse embryos suggested a central role for E2Fs in the control of cell-cycle-dependent gene expression. The analysis of gene expression and E2F-tagged knockin mice with tissue imaging and deep-learning tools suggested that post-transcriptional mechanisms universally coordinate the nuclear accumulation of E2F activators (E2F3A) and canonical (E2F4) and atypical (E2F8) repressors during the cell cycle in vivo. In summary, we mapped the spatiotemporal expression of sentinel E2F activators and canonical and atypical repressors at the single-cell level in vivo and propose that two distinct E2F modules relay the control of gene expression in cells actively cycling (E2F3A-8-4) and exiting the cycle (E2F3A-4) during mammalian development.

Analysis of healthy breast tissue from Komen Tissue Bank shows distinct histology, decreased proliferation, and lower periductal collagen deposition in women with prolonged history of breastfeeding

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Background: Epidemiological studies have shown that prolonged breastfeeding is associated with a reduced risk of developing triple negative/basal-like breast cancer (TN/BLBC). We have modeled abrupt involution (AI) following short breastfeeding and gradual involution (GI) of the mammary gland that occurs over time upon prolonged breastfeeding in wild-type FVB/N mice and discovered prominent histological and molecular changes in the AI glands over time. Further, we demonstrated that breast tissue from healthy women who breastfed <6 months showed enrichment in stem-cell and cell renewal pathways. Here, we corroborate those studies using normal human breast tissue obtained from Susan G. Komen for the Cure Tissue Bank (KTB). Methods: FFPE breast tissue sections obtained from KTB (Protocol #2017CO184). Donors were parous women, aged 18 to 45, without history of breast cancer and for whom breastfeeding history was available. H&E sections and TDLU, the primary anatomical source of most breast cancers, of women who breastfed for ≥6 months (GI, n=49) vs. those who breastfed for ≤3 months (AI, n=20) were evaluated by a blinded pathologist. Masson Trichrome stain was used to measure collagen deposition. Ki67 immunohistochemistry was utilized to determine proliferation. Statistical significance was measured using Fisher’s exact t-test and two-sample t-test with a p-value of <0.05. Results: H&E analysis revealed that breast tissue obtained from women in the AI cohort exhibited histological features of inflammation (p-value= 0.025). Using Ki67 IHC (AI, n=15; GI, n=32) and Masson Trichome stain (AI, n=3; GI, n=4), sections in the AI cohort showed 2-fold increase in proliferation of lobular epithelium (p-value= 0.048) and 1.4-fold increase in periductal collagen deposition (p-value= 0.027) when compared to GI cohort. Age, race, and BMI were not statistically different between AI and GI cohorts. Conclusions: Breast tissue from parous women who breastfed ≤3 months is histologically different than tissue of women with ≥6 months history of breastfeeding. We are currently staining more breast tissue samples obtained from KTB. Experiments are underway to assess the long-term effect of breastfeeding on breast epithelial cell hierarchy and biomarkers of inflammation. Understanding this mechanistic link will help in developing prevention strategies, particularly for African-American women who have lower prevalence of breastfeeding and higher incidence of TN/BLBC.

Abstract P1-09-06: Gene-set enrichment analysis (GSEA) of breast tissue from healthy women with less than six months history of breastfeeding shows enrichment in Hedgehog signaling, notch signaling and luminal progenitor gene signatures

Introduction: Multiple epidemiological studies have shown that prolonged breastfeeding is associated with a reduced risk of developing triple negative/basal-like breast cancer (TN/BLBC). We have modeled abrupt involution (AI) due to lack of breastfeeding and gradual involution (GI) of the mammary gland that occurs over time upon prolonged breastfeeding in wild-type FVB/N mice and discovered prominent histological and molecular changes in the AI glands over time. Our studies revealed for the first time a clear and persistent expansion of mammary luminal progenitor (LP) epithelial cells in AI glands (AACR abstract#2242, 2018). Here, we corroborate animal studies using normal human breast tissue obtained from a reduction mammoplasty tissue collection study (OSU-2011C0094).

Methods: Breast tissue obtained from parous premenopausal women with no history of breast cancer who breastfed for ≥6 months (GI, n=16) versus those who breastfed for &lt;6 months (AI, n=16) (OSU-2011C0094) was used for gene expression analysis. RNA isolated from these normal mammary tissues was analyzed using Affymatrix Gene ChIP Human Transcriptome array 2.0; Gene Set Enrichment Analysis (GSEA) was used to analyze the microarray data. Molecular Signatures Database was used in GSEA querying C2 curated gene sets, Hallmark gene sets, and Lim-Mammary-Luminal-Progenitor gene sets. H&E sections of the breast tissue were used to assess lobular type by counting number of ductules per terminal ductal lobular unit (TDLU). False discovery rate (FDR) q-values and p-values were used for multiple comparison adjustment.

Results: GSEA revealed that breast tissue obtained from women in the AI cohort exhibited strong positive enrichment for Notch and Hedgehog Signaling (Hhg) pathways (FDR q-value= 0.20 and 0.12, respectively). In GI women, GSEA showed an overall trend towards enrichment in metabolic pathways and immune system functions. Moreover, there was non-significant trend towards positive enrichment of mouse LP gene signature in AI women only (FDR q-value= 0.30). Age and BMI were not statistically different between AI and GI cohorts. Analysis of TDLU, the primary anatomical source of most breast cancers, revealed that breast tissue from AI women had proportionally higher lobular type 1 only epithelium than GI women who exhibited more differentiated lobular epithelium (p-value= 0.049).

Conclusion: We report here for the first time that mammary glands from women who breastfed &lt;6 months were enriched for stem-cell signaling pathways and LP gene signature. This reflects some similarity to BRCA1 mutation carriers, who demonstrate expanded luminal progenitor population. In addition, higher Type 1 TDLU's are seen in breast tissue from parous women who breastfed &lt;6 months. Together, these data demonstrate features for TN/BLBC precursors enriched in patients who breastfed for &lt;6 months. Understanding this mechanistic link will help in developing prevention strategies, particularly for African-American women who have lower prevalence of breastfeeding and higher incidence of TN/BLBC.

Citation Format: Basree MM, Shinde N, Palettas M, Weng D, Stover DG, Sizemore GM, Shields P, Majumder S, Ramaswamy B. Gene-set enrichment analysis (GSEA) of breast tissue from healthy women with less than six months history of breastfeeding shows enrichment in Hedgehog signaling, notch signaling and luminal progenitor gene signatures [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-09-06.

Stromal PTEN determines mammary epithelial response to radiotherapy

The importance of the tumor-associated stroma in cancer progression is clear. However, it remains uncertain whether early events in the stroma are capable of initiating breast tumorigenesis. Here, we show that in the mammary glands of non-tumor bearing mice, stromal-specific phosphatase and tensin homolog (Pten) deletion invokes radiation-induced genomic instability in neighboring epithelium. In these animals, a single dose of whole-body radiation causes focal mammary lobuloalveolar hyperplasia through paracrine epidermal growth factor receptor (EGFR) activation, and EGFR inhibition abrogates these cellular changes. By analyzing human tissue, we discover that stromal PTEN is lost in a subset of normal breast samples obtained from reduction mammoplasty, and is predictive of recurrence in breast cancer patients. Combined, these data indicate that diagnostic or therapeutic chest radiation may predispose patients with decreased stromal PTEN expression to secondary breast cancer, and that prophylactic EGFR inhibition may reduce this risk.

Abstract 2242: Breastfeeding protects against pro-tumorigenic changes in the mammary gland by limiting epithelial luminal progenitor cell expansion

Introduction: Multiple epidemiological studies have shown that prolonged breastfeeding is associated with a reduced risk of developing triple-negative/basal-like breast cancers (TN/BLBC). However, no preclinical models that delineate the mechanism of this link exist. This understanding is critical not only to prevent TN/BLBC, but also to address disparity in breast cancer outcomes, as African-American women have a higher incidence of TN/BLBC and lower prevalence of breastfeeding. We present our data using mouse models that provides new insights into this link.

Experimental procedure: We modeled gradual involution (GI) and abrupt involution (AI) of mammary glands (MGs) in wild type FVB/N mice. Uniparous mice were assigned to AI or GI cohorts either by removal of all pups on day7 postpartum (AI) or allowing the pups to naturally wean (GI). MGs were harvested for analysis on postpartum day28, day56 and day120. We assessed MG morphology/histology using whole mounts and H&E stained sections, collagen deposition using Trichrome and PicroSirus red staining, inflammatory markers and immune cell infiltration using immunohistochemistry. Mammary epithelial cell hierarchy was analyzed by Fluorescence-Activated Cell Sorting of a single cell suspension prepared from the MGs. Gene expression was analyzed in mouse mammary epithelial cells using Affymatrix Gene ChIP Mouse Transcriptome array 1.0 and Gene Set Enrichment Analysis (GSEA) was used to analyze gene expression data.

Summary: Abruptly involuted MGs exhibited altered morphology including denser stroma, increased collagen deposition with higher levels of Type I collagen, increased inflammation (pStat3-Y705), increased immune cell infiltration and proliferation compared to GI glands. The mammary epithelial cell hierarchy was disrupted with marked expansion of the luminal progenitor (LP) population in the AI glands but not in the GI glands, a trend frequently observed in women heterozygous for BRCA1 mutation at higher risk of developing BLBC. Enrichment of an LP gene signature and Notch pathway was observed in mouse LP cells isolated from the AI glands. Most strikingly, the AI glands developed alveolar hyperplasia, and squamous metaplasia within 4 months of removal of the pups.

Conclusion: Involution leading to a pro-inflammatory milieu in the MG is well established. Whether involution that happens gradually after prolonged breastfeeding differs in its effect on MGs has not been well studied. Using novel animal modeling to study the differences in MGs following abrupt vs gradual involution, we report a distinct morphology in the mammary tissue favoring pro-carcinogenic changes following AI. Furthermore, we show for the first time, expansion of the LP population in AI glands, which is known to be cell of origin for TN/BLBC potentially linking the risk of TN/BLBC with lack of breastfeeding. Further studies are ongoing.

Citation Format: Mustafa M. Basree, Neelam Shinde, Christopher Koivisto, Maria Cuitino, Raleigh Kladney, Allen Zhang, Hee Kyung Kim, Anthony Trimboli, Jianying Zhang, Gustavo W. Leone, Gina M. Sizemore, Sarmila Majumder, Bhuvaneswari Ramaswamy. Breastfeeding protects against pro-tumorigenic changes in the mammary gland by limiting epithelial luminal progenitor cell expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2242.

E2f8 mediates tumor suppression in postnatal liver development

E2F-mediated transcriptional repression of cell cycle-dependent gene expression is critical for the control of cellular proliferation, survival, and development. E2F signaling also interacts with transcriptional programs that are downstream of genetic predictors for cancer development, including hepatocellular carcinoma (HCC). Here, we evaluated the function of the atypical repressor genes E2f7 and E2f8 in adult liver physiology. Using several loss-of-function alleles in mice, we determined that combined deletion of E2f7 and E2f8 in hepatocytes leads to HCC. Temporal-specific ablation strategies revealed that E2f8's tumor suppressor role is critical during the first 2 weeks of life, which correspond to a highly proliferative stage of postnatal liver development. Disruption of E2F8's DNA binding activity phenocopied the effects of an E2f8 null allele and led to HCC. Finally, a profile of chromatin occupancy and gene expression in young and tumor-bearing mice identified a set of shared targets for E2F7 and E2F8 whose increased expression during early postnatal liver development is associated with HCC progression in mice. Increased expression of E2F8-specific target genes was also observed in human liver biopsies from HCC patients compared to healthy patients. In summary, these studies suggest that E2F8-mediated transcriptional repression is a critical tumor suppressor mechanism during postnatal liver development.

Therapeutic Effects of Oral Nutritional Supplements during Haemodialysis: Physician's Experience

OBJECTIVES

To evaluate the effects of predialytic oral nutritional supplementation in chronic kidney disease (CKD) patients on maintenance haemodialysis (MHD).

METHODS

NEPRO HP was provided to 77 CKD patients on maintenance haemodialysis (MHD) over 3 months. Efficacy parameters were improvement in albumin levels, weight and haemoglobin levels; safety parameters were serum potassium and phosphorus values; other parameters were SGA and MIS scores.

RESULTS

Mean serum albumin values showed a statistically significant increase. There was a statistically significant improvement in the mean body weight and haemoglobin of the patients in the second and third months of treatment. Serum phosphorus and potassium levels did not change in a statistically significant manner. There was improvement in nourishment status as detected by MIS and SGA scores. Two patients expired during the course of the study.

CONCLUSION

Predialytic oral supplementation with NEPRO HP improves nutritional status of CKD patients on MHD.

Declining seroprevalence of HIV infection among paediatric inpatients

An unlinked anonymous testing for HIV infection among consecutive paediatric admissions at Cama and Albless Hospital, Mumbai, was performed in 1998-99 and again in 2003-04. The seroprevalence declined from 5.5% (24/535) to 2.2% (10/447). Greater awareness, enhanced antenatal detection and measures taken to prevent mother-to-child transmission (MTCT) seem to have contributed to the declining seroprevalence. We believe that paediatric inpatients reflect the extent of MTCT in the community.