SnapShot: FABP Functions.

Fatty acid binding proteins (FABPs) serve as intracellular chaperones for fatty acids and other hydrophobic ligands inside cells. Recent studies have demonstrated new functions of individual members of the FABP family. This Snapshot describes the overall functions of FABPs in health and disease and highlights emerging roles of adipose FABP (A-FABP) and epidermal FABP (E-FABP) in the fields of obesity, chronic inflammation, and cancer development. To view this SnapShot, open or download the PDF.

Stearic Acid Induces CD11c Expression in Proinflammatory Macrophages via Epidermal Fatty Acid Binding Protein.

Obesity is associated with elevated levels of free fatty acids (FAs) and proinflammatory CD11c+ macrophages. However, whether and how free FAs contribute to CD11c+ macrophage differentiation and proinflammatory functions remain unclear. Here we report that dietary saturated FAs, but not unsaturated FAs, promoted the differentiation and function of CD11c+ macrophages. Specifically, we demonstrated that stearic acid (SA) significantly induced CD11c expression in monocytes through activation of the nuclear retinoid acid receptor. More importantly, cytosolic expression of epidermal FA binding protein (E-FABP) in monocytes/macrophages was shown to be critical to the mediation of the SA-induced effect. Depletion of E-FABP not only inhibited SA-induced CD11c upregulation in macrophages in vitro but also abrogated high-saturated-fat diet-induced skin lesions in obese mouse models in vivo. Altogether, our data demonstrate a novel mechanism by which saturated FAs promote obesity-associated inflammation through inducing E-FABP/retinoid acid receptor-mediated differentiation of CD11c+ macrophages.

Adipose Fatty Acid Binding Protein Promotes Saturated Fatty Acid-Induced Macrophage Cell Death through Enhancing Ceramide Production.

Macrophages play a critical role in obesity-associated chronic inflammation and disorders. However, the molecular mechanisms underlying the response of macrophages to elevated fatty acids (FAs) and their contribution to metabolic inflammation in obesity remain to be fully elucidated. In this article, we report a new mechanism by which dietary FAs, in particular, saturated FAs (sFAs), are able to directly trigger macrophage cell death. We demonstrated that excess sFAs, but not unsaturated FAs, induced the production of cytotoxic ceramides (Cers) in macrophage cell lines. Most importantly, expression of adipose FA binding protein (A-FABP) in macrophages facilitated metabolism of excess sFAs for Cer synthesis. Inhibition or deficiency of A-FABP in macrophage cell lines decreased sFA-induced Cer production, thereby resulting in reduced cell death. Furthermore, we validated the role of A-FABP in promoting sFA-induced macrophage cell death with primary bone marrow-derived macrophages and high-fat diet-induced obese mice. Altogether, our data reveal that excess dietary sFAs may serve as direct triggers in induction of Cer production and macrophage cell death through elevated expression of A-FABP, thus establishing A-FABP as a new molecular sensor in triggering macrophage-associated sterile inflammation in obesity.

Protease-activated Receptor-2 (PAR-2)-mediated Nf-κB Activation Suppresses Inflammation-associated Tumor Suppressor MicroRNAs in Oral Squamous Cell Carcinoma.

Oral cancer is the sixth most common cause of death from cancer with an estimated 400,000 deaths worldwide and a low (50%) 5-year survival rate. The most common form of oral cancer is oral squamous cell carcinoma (OSCC). OSCC is highly inflammatory and invasive, and the degree of inflammation correlates with tumor aggressiveness. The G protein-coupled receptor protease-activated receptor-2 (PAR-2) plays a key role in inflammation. PAR-2 is activated via proteolytic cleavage by trypsin-like serine proteases, including kallikrein-5 (KLK5), or by treatment with activating peptides. PAR-2 activation induces G protein-α-mediated signaling, mobilizing intracellular calcium and Nf-κB signaling, leading to the increased expression of pro-inflammatory mRNAs. Little is known, however, about PAR-2 regulation of inflammation-related microRNAs. Here, we assess PAR-2 expression and function in OSCC cell lines and tissues. Stimulation of PAR-2 activates Nf-κB signaling, resulting in RelA nuclear translocation and enhanced expression of pro-inflammatory mRNAs. Concomitantly, suppression of the anti-inflammatory tumor suppressor microRNAs let-7d, miR-23b, and miR-200c was observed following PAR-2 stimulation. Analysis of orthotopic oral tumors generated by cells with reduced KLK5 expression showed smaller, less aggressive lesions with reduced inflammatory infiltrate relative to tumors generated by KLK5-expressing control cells. Together, these data support a model wherein KLK5-mediated PAR-2 activation regulates the expression of inflammation-associated mRNAs and microRNAs, thereby modulating progression of oral tumors.

Complex-I Alteration and Enhanced Mitochondrial Fusion Are Associated With Prostate Cancer Progression.

Mitochondria (mt) encoded respiratory complex-I (RCI) mutations and their pathogenicity remain largely unknown in prostate cancer (PCa). Little is known about the role of mtDNA loss on mt integrity in PCa. We determined mtDNA mutation in human and mice PCa and assessed the impact of mtDNA depletion on mt integrity. We also examined whether the circulating exosomes from PCa patients are transported to mt and carry mtDNA or mt proteins. We have employed next generation sequencing of the whole mt genome in human and Hi-myc PCa. The impact of mtDNA depletion on mt integrity, presence of mtDNA, and protein in sera exosomes was determined. A co-culture of human PCa cells and the circulating exosomes followed by confocal imaging determined co-localization of exosomes and mt. We observed frequent RCI mutations in human and Hi-myc PCa which disrupted corresponding complex protein expression. Depletion of mtDNA in PCa cells influenced mt integrity, increased expression of MFN1, MFN2, PINK1, and decreased expression of MT-TFA. Increased mt fusion and expression of PINK1 and DNM1L were also evident in the Hi-myc tumors. RCI-mtDNA, MFN2, and IMMT proteins were detected in the circulating exosomes of men with benign prostate hyperplasia (BPH) and progressive PCa. Circulating exosomes and mt co-localized in PCa cells. Our study identified new pathogenic RCI mutations in PCa and defined the impact of mtDNA loss on mt integrity. Presence of mtDNA and mt proteins in the circulating exosomes implicated their usefulness for biomarker development.

Effects of energy deficit, dietary protein, and feeding on intracellular regulators of skeletal muscle proteolysis.

This study was undertaken to characterize the ubiquitin proteasome system (UPS) response to varied dietary protein intake, energy deficit (ED), and consumption of a mixed meal. A randomized, controlled trial of 39 adults consuming protein at 0.8 (recommended dietary allowance [RDA]), 1.6 (2×-RDA), or 2.4 (3×-RDA) g · kg(-1) · d(-1) for 31 d. A 10-d weight maintenance (WM) period was followed by 21 d of 40% ED. Ubiquitin (Ub)-mediated proteolysis and associated gene expression were assessed in the postabsorptive (fasted) and postprandial (fed; 480 kcal, 20 g protein) states after WM and ED by using muscle biopsies, fluorescence-based assays, immunoblot analysis, and real-time qRT-PCR. In the assessment of UPS responses to varied protein intakes, ED, and feeding, the RDA, WM, and fasted measures served as appropriate controls. ED resulted in the up-regulation of UPS-associated gene expression, as mRNA expression of the atrogenes muscle RING finger-1 (MuRF1) and atrogin-1 were 1.2- and 1.3-fold higher (P<0.05) for ED than for WM. However, mixed-meal consumption attenuated UPS-mediated proteolysis, independent of energy status or dietary protein, as the activities of the 26S proteasome subunits ß1, ß2, and ß5 were lower (P<0.05) for fed than for fasted. Muscle protein ubiquitylation was also 45% lower (P<0.05) for fed than for fasted, regardless of dietary protein and energy manipulations. Independent of habitual protein intake and despite increased MuRF1 and atrogin-1 mRNA expression during ED, consuming a protein-containing mixed meal attenuates Ub-mediated proteolysis.

Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial.

The purpose of this work was to determine the effects of varying levels of dietary protein on body composition and muscle protein synthesis during energy deficit (ED). A randomized controlled trial of 39 adults assigned the subjects diets providing protein at 0.8 (recommended dietary allowance; RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g kg(-1) d(-1) for 31 d. A 10-d weight-maintenance (WM) period was followed by a 21 d, 40% ED. Body composition and postabsorptive and postprandial muscle protein synthesis were assessed during WM (d 9-10) and ED (d 30-31). Volunteers lost (P<0.05) 3.2 ± 0.2 kg body weight during ED regardless of dietary protein. The proportion of weight loss due to reductions in fat-free mass was lower (P<0.05) and the loss of fat mass was higher (P<0.05) in those receiving 2×-RDA and 3×-RDA compared to RDA. The anabolic muscle response to a protein-rich meal during ED was not different (P>0.05) from WM for 2×-RDA and 3×-RDA, but was lower during ED than WM for those consuming RDA levels of protein (energy × protein interaction, P<0.05). To assess muscle protein metabolic responses to varied protein intakes during ED, RDA served as the study control. In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss.

Methylation and miRNA effects of resveratrol on mammary tumors vs. normal tissue.

We reported that resveratrol decreased DNA methyltransferase (DNMT) 1 and 3b expression in vitro and demethylates tumor suppressor RASSF-1a in women at increased breast cancer risk. We investigated the effects of resveratrol on DNMT and miRNA expression in normal and tumor mammary tissue in a rodent model of estrogen dependent mammary carcinoma. Eighty-nine female ACI rats received estradiol plus: low dose (lo) resveratrol, high dose (hi) resveratrol, 5-aza-2-deoxycytidine (Aza), a known inhibitor of DNMTs, or control (no additional treatment). After 21 wk of treatment, animals were sacrificed and mammary glands harvested. Matched tumor/normal tissues were available from 36 rats. DMNT3b (but not DNMT1) differed in tumor vs. normal tissue after lo (P = .04) and hi (P = .007) resveratrol and Aza treatment. With hi resveratrol, DNMT3b decreased in tumor but increased normal tissue. Hi resveratrol increased miR21, -129, -204, and -489 >twofold in tumor and decreased the same miRs in normal tissue 10-50% compared to control. There was an inverse association between DNMT3b and miR129, -204, and -489 in normal and/or tumor tissue. Treatment with resveratrol differentially influences tumor vs. normal tissue DNMT3b and miRNA expression. This mechanism of action of resveratrol to influence mammary carcinogenesis warrants further investigation.

Mechanisms by Which Pharmacotherapy May Impact Cancer Risk among Individuals with Overweight and Obesity.

Diets geared to reduce cancer risk in overweight and obese individuals focus on (1) caloric restriction (every day, some days, or most hours of each day); (2) changes in macronutrient intake; or (3) a combination of the prior two strategies. Diets generally fail because of nonadherence or due to limited sustained weight loss. This is in contrast to a diet supplemented with a weight loss medication, so long as the participant continues the medication or after bariatric surgery, in which adherence tends to be much higher. Among individuals who regain weight after surgery, weight loss medications are proving beneficial in maintaining weight loss. Both maximum and sustained weight loss are essential for all forms of effective metabolic improvement, including cancer risk reduction. The focus of this report is to assess the state of research on the consequence of pharmacotherapy use on weight loss and proposed weight loss-independent effects on subsequent cancer risk reduction, including the potential role of medication use in conjunction with metabolic (bariatric) surgery (MBS). Finally, we present Notices of Funding Opportunities (NOFOs) by the National Cancer Institute (NCI) to better understand the mechanism(s) that are driving the efficacy of pharmacotherapy in cancer risk reduction.

Natural Products for Cancer Prevention and Interception: Preclinical and Clinical Studies and Funding Opportunities.

Multiple agents derived from natural products (NPs) have been evaluated for cancer prevention and interception, either alone or in combination. The National Cancer Institute (NCI) is very interested in advancing research to identify additional agents that, alone or in combination, may prove useful in cancer prevention. Below, we provide an overview of NP studies in cancer prevention and interception, both individual agents and combination interventions. Given that findings from many preclinical studies evaluating individual agents have generally not been confirmed in human studies, our focus with individual NPs in this review is on studies involving humans, especially clinical trials. Fewer combination intervention studies have been conducted, so we have broadened our review to include preclinical studies. We conclude with how the Division of Cancer Prevention (DCP) within the NCI is providing funding to encourage the research community to propose natural product studies in cancer prevention and interception to advance the field.

Long-Term Randomized Controlled Trials of Diet Intervention Reports and Their Impact on Cancer: A Systematic Review.

BACKGROUND: Most randomized controlled trials (RCTs) assessing the impact of diet on cancer have been short term (<1 year), mostly evaluating breast cancer survivors. Given the many-year interval that is generally required for an intervention to have an impact on cancer risk or prognosis, as well as the fact that lifestyle strategies such as diet modification frequently fail due to lack of adherence over the long term, we focused this systematic review only on longer-term (≥1 year) intervention reports. Diet intervention reports focused on reducing cancer risk in overweight and obese individuals target caloric restriction (every day, some days, or most hours of each day). METHODS: This study is a systematic review of RCTs lasting at least 1 year, testing dietary interventions with a primary or secondary endpoint of cancer or a biomarker linked to cancer. RESULTS: Fifty-one reports met our review criteria. Twenty of fifty-one (39%) reports are RCTs where the primary endpoint was cancer or a cancer-related biomarker, while the other reports evaluated reports where cancer or a cancer-related biomarker was a secondary endpoint. Thirteen of twenty (65%) primary reports evaluated isocaloric, and the remaining eight evaluated low-calorie diets. All but one of the primary and two secondary isocaloric diet reports evaluated the benefit of a low-fat diet (LFD), with the other three evaluating a Mediterranean diet (MedD). More LCD vs. isocaloric diet primary reports (71% vs. 38%) demonstrated cancer or cancer-related biomarker benefit; the difference in chance of benefit with secondary reports was 85% for LCD vs. 73% for isocaloric diets. Three of three MedD reports demonstrated benefit. Sixty-nine percent (20/29) of the secondary reports came from two large reports: the WHI diet modification trial (15 secondary reports) and the polyp prevention trial (5 secondary reports). Nineteen of twenty-two (86%) primary reports enrolled only women, and three enrolled both men and women. No study that met our criteria enrolled only men, comprising 1447 men in total vs. 62,054 women. Fifteen of twenty (75%) primary reports focus on healthy women or women with breast cancer. Adherence findings are discussed when provided. CONCLUSIONS: More long-term RCTs evaluating cancer and cancer-related biomarker endpoints are needed, especially for cancers at sites other than the breast.

Metabolic Dysregulation and Cancer Risk Program (MeDOC): a transdisciplinary approach to obesity-associated cancers.

With the escalating prevalence of obesity, the association between obesity and cancer is a growing public health concern. Obesity will soon surpass tobacco smoking as the most important preventable cause of cancer. Obesity-driven mechanisms can alter cell functions to induce metabolic changes, chronic inflammation, and insulin resistance that are believed to contribute to cancer risk and development; yet the specific underlying biological mechanisms of obesity-related cancer development are largely unknown. The Metabolic Dysregulation and Cancer Risk Program: a transdisciplinary approach to obesity-associated cancers (MeDOC) is a trans-National Cancer Institute research initiative supported by the Division of Cancer Control and Population Sciences, the Division of Cancer Biology, the Division of Cancer Prevention, and the Center to Reduce Cancer Health Disparities. The overall purpose of the MeDOC Program is to advance our understanding of the underlying mechanisms that connect obesity, metabolic dysregulation, and increased obesity cancer risk as well as identify markers that will enhance cancer risk prediction, improve screening for high-risk individuals, and identify targets for preventive and therapeutic interventions for cancer interception or treatment. This report describes the funded research projects, the Coordinating Center, and the goals of the MeDOC program.

FABP4-mediated lipid accumulation and lipolysis in tumor associated macrophages promote breast cancer metastasis.

A high density of tumor-associated macrophages (TAMs) is associated with poorer prognosis and survival in breast cancer patients. Recent studies have shown that lipid accumulation in TAMs can promote tumor growth and metastasis in various models. However, the specific molecular mechanisms that drive lipid accumulation and tumor progression in TAMs remain largely unknown. Herein, we demonstrated that unsaturated fatty acids (FAs), unlike saturated ones, are more likely to form lipid droplets in macrophages. Specifically, unsaturated FAs, including linoleic acids (LA), activate the FABP4/CEBPα pathway, leading to triglyceride synthesis and lipid droplet formation. Furthermore, FABP4 enhances lipolysis and FA utilization by breast cancer cells, which promotes cancer cell migration in vitro and metastasis in vivo . Notably, a deficiency of FABP4 in macrophages significantly reduces LA-induced lipid metabolism. Therefore, our findings suggest FABP4 as a crucial lipid messenger that facilitates unsaturated FA-mediated lipid accumulation and lipolysis in TAMs, thus contributing to the metastasis of breast cancer. Highlights: Unlike saturated fatty acids, unsaturated fatty acids preferentially promote lipid droplet formation in macrophages.Unsaturated fatty acids activate the FABP4/CEBPα axis for neutral lipid biosynthesis in macrophagesDeficiency of FABP4 compromised unsaturated fatty acid-mediated lipid accumulation and utilization in macrophagesFABP4-mediated lipid metabolism in macrophages contributes to breast cancer metastasis.

Elastin turnover in malignant solid tumors.

Desmosine, a crosslinking amino acid unique to elastin, was investigated as a possible biomarker for cancer. Twenty-eight normal controls, median age 67 years, had a median value for urine desmosine of 43.5 picomoles desmosine/mg creatinine. The median for 19 untreated cancer subjects of similar age was significantly higher (175 picomoles desmosine/mg creatinine, p < 0.001). Urine desmosine levels in 55 subjects currently receiving chemotherapy, as well as 67 individuals who had survived cancer and were currently clinically disease free, were not significantly different from controls. Our findings indicate that elastin is being turned over in malignant solid tumors, releasing significantly elevated levels of desmosine in the urine.

Obesity, metabolic and bariatric surgery, and cancer prevention: what do we need to learn and how do we get there?

Obesity and associated metabolic dysfunction are on the rise in the United States and around the world. Metabolic dysfunction often leads to chronic disease, including cancer. Recent evidence suggests that weight loss among individuals with obesity may decrease cancer risk. Metabolic and bariatric surgery (MBS) leads to greater maximum and sustained weight loss than nonsurgical dietary strategies and demonstrates the most convincing evidence that weight loss lowers cancer risk. Caloric restriction diets combined with GLP-1 receptor agonists demonstrate weight loss intermediate between MBS and other nonsurgical diet strategies so long as individuals consistently take the medication. Weight regain after initial loss is a major problem with all weight loss strategies. To better prevent cancer in individuals with obesity, we need to individualize weight loss strategies, determining what strategy works for a given individual and how to implement it. We need to learn (1) what an individual's impediments to initial and sustained weight loss are; (2) what the optimal weight loss strategy, be it diet modification, diet modification + medication, or MBS followed by diet modification, is; (3) how exercise(s) should be incorporated into weight loss strategies; (4) where medications fit into the treatment strategy of individuals with obesity; and (5) what the mechanisms driving the influence of MBS on cancer risk are. We also need to (6) explore expanding the eligibility of MBS to individuals with a body mass index <35 kg/m2. Answers to these questions require a better understanding of how MBS impacts cancer risk, including in which groups (women versus men, which racial and ethnic groups, which cancers, which MBS procedure) MBS works best to reduce risk. The National Cancer Institute, through new funding opportunities, hopes to advance our understanding of how obesity drives cancer risk and how individuals with obesity can prevent cancer development and, among those with cancer, prevent disease recurrence.

Role of FABP5 in T Cell Lipid Metabolism and Function in the Tumor Microenvironment.

To evade immune surveillance, tumors develop a hostile microenvironment that inhibits anti-tumor immunity. Recent immunotherapy breakthroughs that target the reinvigoration of tumor-infiltrating T lymphocytes (TIL) have led to unprecedented success in treating some cancers that are resistant to conventional therapy, suggesting that T cells play a pivotal role in anti-tumor immunity. In the hostile tumor microenvironment (TME), activated T cells are known to mainly rely on aerobic glycolysis to facilitate their proliferation and anti-tumor function. However, TILs usually exhibit an exhausted phenotype and impaired anti-tumor activity due to the limited availability of key nutrients (e.g., glucose) in the TME. Given that different T cell subsets have unique metabolic pathways which determine their effector function, this review introduces our current understanding of T cell development, activation signals and metabolic pathways. Moreover, emerging evidence suggests that fatty acid binding protein 5 (FABP5) expression in T cells regulates T cell lipid metabolism and function. We highlight how FABP5 regulates fatty acid uptake and oxidation, thus shaping the survival and function of different T cell subsets in the TME.

Feasibility of 5-fluorouracil and imiquimod for the topical treatment of cervical intraepithelial neoplasias (CIN) 2/3.

OBJECTIVES: To determine the feasibility (as measured by tolerability and safety) and efficacy of topical 5-fluorouracil (5-FU) and imiquimod for the treatment of cervical intraepithelial neoplasia (CIN) 2/3. METHODS: This pilot prospective study was conducted in women aged 18-45 years with p16+ CIN 2/3. Participants underwent an 8-week alternating regimen of self-applied 5% 5-FU on weeks 1, 3, 5, and 7 and physician-applied imiquimod on weeks 2, 4, 6, and 8. Adverse events (AEs) were collected by symptom diary and clinical exam. Feasibility was measured by tolerability and safety (AEs) of the study intervention. Tolerability was assessed as the number of participants able to apply 50% or more of the treatment doses. The safety outcome was calculated as the number of participants who experienced "specified AEs" defined as possibly, probably, or definitely related grade 2 or worse AE or grade 1 genital AEs (blisters, ulcerations, or pustules) lasting more than 5 days. The efficacy of the intervention was determined by histology and high-risk human papillomavirus (hrHPV) testing was done after treatment. RESULTS: The median age of the 13 participants was 27 ± 2.9 years. Eleven (84.61%) participants applied 50% or more of the treatment. All participants reported grade 1 AEs; 6 (46.15%) reported grade 2 AEs; and 0 reported grade 3/4 AEs. Three (23.08%) participants had specified AEs. Histologic regression to normal or CIN 1 among those completing 50% or more of the treatment doses was observed in 10 (90.91%) participants, and 7 (63.63%) tested negative for hr-HPV at the end of the study. CONCLUSIONS: Topical treatment for CIN 2/3 with 5-FU/imiquimod is feasible, with preliminary evidence of efficacy. Topical therapies need further investigation as adjuncts or alternatives to surgical therapy for CIN 2/3.

Proteins and carbohydrates in nipple aspirate fluid predict the presence of atypia and cancer in women requiring diagnostic breast biopsy.

BACKGROUND: Herein we present the results of two related investigations. The first study determined if concentrations in breast nipple discharge (ND) of two proteins (urinary plasminogen activator, uPA and its inhibitor, PAI-1) predicted the presence of breast atypia and cancer in pre- and/or postmenopausal women requiring surgery because of a suspicious breast lesion. The second study assessed if these proteins increased the predictive ability of a carbohydrate (Thomsen Friedenreich, TF) which we previously demonstrated predicted the presence of disease in postmenopausal women requiring surgery. METHODS: In the first study we prospectively enrolled 79 participants from whom we collected ND, measured uPA and PAI-1 and correlated expression with pathologic findings. In the second study we analyzed 35 (uPA and PAI-1 in 24, uPA in an additional 11) ND samples collected from different participants requiring breast surgery, all of whom also had TF results. RESULTS: uPA expression was higher in pre- and PAI-1 in postmenopausal women with 1) cancer (DCIS or invasive) vs. either no cancer (atypia or benign pathology, p = .018 and .025, respectively), or benign pathology (p = .017 and .033, respectively); and 2) abnormal (atypia or cancer) versus benign pathology (p = .018 and .052, respectively). High uPA and PAI-1 concentrations and age were independent predictors of disease in premenopausal women, with an area under the curve (AUC) of 83-87% when comparing diseased vs. benign pathology. uPA, TF, and age correctly classified 35 pre- and postmenopausal women as having disease or not 84-91% of the time, whereas combining uPA+PAI-1+TF correctly classified 24 women 97-100% of the time. CONCLUSIONS: uPA and PAI-1 concentrations in ND were higher in women with atypia and cancer compared to women with benign disease. Combining uPA, PAI-1 and TF in the assessment of women requiring diagnostic breast surgery maximized disease prediction. The assessment of these markers may prove useful in early breast cancer detection.

Differential expression of cancer associated proteins in breast milk based on age at first full term pregnancy.

BACKGROUND: First full term pregnancy (FFTP) completed at a young age has been linked to low long term breast cancer risk, whereas late FFTP pregnancy age confers high long term risk, compared to nulliparity. Our hypothesis was that proteins linked to breast cancer would be differentially expressed in human milk collected at three time points during lactation based on age at FFTP. METHODS: We analyzed breast milk from 72 lactating women. Samples were collected within 10 days of the onset of lactation (baseline-BL), two months after lactation started and during breast weaning (W). We measured 16 proteins (11 kallikreins (KLKs), basic fibroblast growth factor, YKL-40, neutrophil gelatinase-associated lipocalin and transforming growth factor (TGF) ß-1 and -2) associated with breast cancer, most known to be secreted into milk. RESULTS: During lactation there was a significant change in the expression of 14 proteins in women < 26 years old and 9 proteins in women > = 26 at FFTP. The most significant (p < .001) changes from BL to W in women divided by FFTP age (< 26 vs. > = 26) were in KLK3,6, 8, and TGFß2 in women < 26; and KLK6, 8, and TGFß2 in women > = 26. There was a significant increase (p = .022) in KLK8 expression from BL to W depending on FFTP age. Examination of DNA methylation in the promoter region of KLK6 revealed high levels of methylation that did not explain the observed changes in protein levels. On the other hand, KLK6 and TGFß1 expression were significantly associated (r2 = .43, p = .0050). CONCLUSIONS: The expression profile of milk proteins linked to breast cancer is influenced by age at FFTP. These proteins may play a role in future cancer risk.