Chris E. Holmes

The platelet contribution to cancer progression

Summary.  Traditionally viewed as major cellular components in hemostasis and thrombosis, the contribution of platelets to the progression of cancer is an emerging area of research interest. Complex interactions between tumor cells and circulating platelets play an important role in cancer growth and dissemination, and a growing body of evidence supports a role for physiologic platelet receptors and platelet agonists in cancer metastases and angiogenesis. Platelets provide a procoagulant surface facilitating amplification of cancer‐related coagulation, and can be recruited to shroud tumor cells, thereby shielding them from immune responses, and facilitate cancer growth and dissemination. Experimental blockade of key platelet receptors, such as GP1b/IX/V, GPIIbIIIa and GPVI, has been shown to attenuate metastases. Platelets are also recognized as dynamic reservoirs of proangiogenic and anti‐angiogenic proteins that can be manipulated pharmacologically. A bidirectional relationship between platelets and tumors is also seen, with evidence of ‘tumor conditioning’ of platelets. The platelet as a reporter of malignancy and a targeted delivery system for anticancer therapy has also been proposed. The development of platelet inhibitors that influence malignancy progression and clinical testing of currently available antiplatelet drugs represents a promising area of targeted cancer therapy.

Diagnosis and Treatment of Breast Cancer in the Elderly

As the population of the United States ages, women over the age of 65 have become a prominent cohort in the breast cancer population, with approximately 50% of all new breast cancers occurring in women aged 65 years and older. Early studies in breast cancer often excluded women based on age or comorbidity, leaving physicians and patients with a growing number of diagnostic and treatment options, each of which often carry short‐term morbidity risks for potential long‐term gain. We review the current data available for diagnosis and treatment of elderly women with breast cancer in both the adjuvant and metastatic disease setting. In addition, the role of screening and new concepts in prevention are discussed with emphasis on the older patient.

Platelets in Tumor Progression: A Host Factor That Offers Multiple Potential Targets in the Treatment of Cancer

While platelets are well known to play a central role in hemostasis and thrombosis, there is emerging experimental evidence to suggest that they also mediate tumor cell growth, dissemination, and angiogenesis. An increase in platelet number (thrombocytosis) and activity is seen in patients with a wide spectrum of malignancies, and the former is correlated with a decrease in overall survival and poorer prognosis. Preclinical data suggest that circulating tumor cell partnerships with platelets in the blood facilitate tumor metastases through direct interactions and secreted bioactive proteins. Platelets form aggregates with tumor cells, thereby protecting them from host immune surveillance through physical shielding and induction of “platelet mimicry.” There is also laboratory evidence to suggest that activated platelets interact with cancer cells within the tumor microenvironment through paracrine signaling and direct contact, thereby promoting tumor cell growth and survival. For example, platelets release mediators of both tumor angiogenesis and osteoclast resorption. The interplay between platelets and tumor cells is complex and bidirectional with involvement of multiple other components within the tumor microenvironment, including immune cells, endothelial cells, and the extracellular matrix. We review the role of platelets in tumor progression, emphasizing the opportunity these interactions afford to target platelets and platelet function to improve patient outcomes in the cancer prevention and treatment setting. J. Cell. Physiol. 229: 1005–1015, 2014.

The effect of P2Y-mediated platelet activation on the release of VEGF and endostatin from platelets.

Vascular endothelial growth factor (VEGF) and endostatin are key protein modulators of angiogenesis found within platelets. The platelet activation pathways that control angiogenic protein release are incompletely elucidated. The differential release of pro-angiogenic and anti-angiogenic proteins from the platelet has been demonstrated for proteinase activated receptors (PARs). Given the ability of tumors to secrete ADP and the availability of ADP receptor antagonists clinically, we determined the influence of adenosine diphosphate (ADP) and the ADP receptors, P2Y1 and P2Y12, on platelet release of the angiogenic stimulator protein, VEGF, and the angiogenic inhibitor protein, endostatin. Minimally altered whole blood (WB) and platelet rich plasma (PRP) from healthy volunteers was stimulated with ADP alone (12.5 uM), in combination with a P2Y1 antagonist (MRS2179) or a P2Y12 antagonist (cangrelor). VEGF and endostatin protein concentrations were assessed by an ELISA assay. We report that maximally stimulating concentrations of ADP significantly increased VEGF release from platelets in both PRP and WB by 36+/−12% 36+/−12% 54+/−18% 36 ± 12% (p < 0.05) respectively as compared to control. Both P2Y1 and P2Y12 receptor antagonism inhibited this release. Conversely, endostatin levels did not change following ADP stimulation in PRP, while a 4.7% (p = 0.03) increase was observed in WB. As compared to thrombin receptor activation, ADP activation was a weaker stimulus for VEGF release. We found that activation of platelets by ADP results in an increase in soluble VEGF concentrations with minimal effects on endostatin concentrations, suggesting ADP release in the tumor microenvironment may be, on balance, proangiogenic. P2Y receptor antagonism abrogates ADP mediated proangiogenic protein release and thus may represent a potential pharmacologic strategy for regulating platelet mediated angiogenesis.

Platelet count and the risk for thrombosis and death in the elderly

Summary.  Aim: Our aim was to examine the association between platelet count and the incidence of myocardial infarction, ischemic stroke, hemorrhagic stroke, venous thrombosis, and mortality. Methods and results: Platelet count was measured at baseline in 1989–1990 and at 3 years follow‐up, or at baseline (for a newly recruited group) in 1992–1993 in 5766 community‐dwelling individuals aged 65 years and older (mean age at baseline, 73 years). During 12–15 years of follow‐up, there were 821 incident myocardial infarctions, 807 ischemic strokes, 161 hemorrhagic strokes, 159 venous thrombotic events, and 3413 participants died. Platelet count was not associated with the occurrence of myocardial infarction, ischemic or hemorrhagic stroke, venous thrombosis, or cardiovascular mortality. Non‐cardiovascular mortality was higher among both participants with low and with high platelet count. Adjusted non‐cardiovascular mortality rates for platelet counts below 100, 100–199, 300–399, and above 400 × 109 L−1 relative to the reference mortality rate in participants with platelet count values between 200 and 299 × 109 L−1 were 1.89 (1.21–2.96), 1.08 (0.98–1.20), 1.20 (1.06–1.37), and 1.47 (1.14–1.90), respectively. Conclusion: Platelet counts were not associated with vascular outcomes but low and high platelet counts were associated with non‐cardiovascular mortality, including cancer mortality.

Platelets, coagulation and fibrinolysis in breast cancer progression.

The progression of breast cancer from early-stage to metastatic disease results from a series of events during which malignant cells invade and travel within the bloodstream to distant sites, leading to a clonogenic accumulation of tumor cells in non-breast tissue. While mechanistically complex, an emerging literature supports hemostatic elements as an important patient factor that facilitates the metastatic potential of breast cancer. Hemostatic elements involved include platelets, coagulation, and fibrinolysis. Key steps in breast tumor progression, including cellular transformation, proliferation, tumor cell survival, and angiogenesis, can be mediated by components of the hemostatic system. Thus, the hemostatic system provides potential targets for novel therapeutic approaches to breast cancer therapy with drugs in current use and in development. The present article provides a comprehensive overview of the evidence and mechanisms supporting the roles played by platelets, coagulation activation, and the fibrinolytic system in breast cancer progression.

Correlates of Anemia in American Blacks and Whites The REGARDS Renal Ancillary Study

For unclear reasons, anemia is more common in American blacks than whites. The authors evaluated anemia prevalence (using World Health Organization criteria) among 19,836 blacks and whites recruited in 2003-2007 for the REasons for Geographic And Racial Differences in Stroke Renal Ancillary study and characterized anemia by 3 anemia-associated conditions (chronic kidney disease, inflammation, and microcytosis). They used multivariable models to assess potential causes of race differences in anemia. Anemia was 3.3-fold more common in blacks than whites, with little attenuation after adjusting for demographic variables, socioeconomic factors, and comorbid conditions. Increasing age, residence in the US southeast, lower income, vascular disease, diabetes, hypertension, and never smoking were associated with anemia. Age, diabetes, and vascular disease were stronger correlates of anemia among whites than blacks (P < 0.05). Among those with anemia, chronic kidney disease was less common among blacks than whites (22% vs. 34%), whereas inflammation (18% vs. 14%) and microcytosis (22% vs. 11%) were more common. In this large, geographically diverse cohort, anemia was 3-fold more common in blacks than whites with different characteristics and correlates. Race differences in anemia prevalence were not explained by the factors studied. Future research into the causes and consequences of anemia in different racial groups is needed.

Tamoxifen and Aromatase Inhibitors Differentially Affect Vascular Endothelial Growth Factor and Endostatin Levels in Women with Breast Cancer

Purpose: Circulating and cellular proangiogenic and antiangiogenic proteins such as vascular endothelial growth factor (VEGF) and endostatin contribute to the local angiogenic balance. We explored the effects of tamoxifen and aromatase inhibitors on concentrations of VEGF and endostatin in plasma, serum, and platelet releasate (induced by platelet activation). Experimental Design: VEGF and endostatin concentrations were measured with a quantitative immunoassay before and after 1 to 5 weeks of treatment in 30 women with breast cancer treated with either tamoxifen (n = 14) or aromatase inhibitors (n = 16). Platelet activation was induced by a thrombin receptor agonist. Results: Tamoxifen therapy resulted in an increase in platelet releasate concentrations of VEGF (P = 0.01) but no change in plasma VEGF. In contrast, aromatase inhibitor therapy did not affect serum, plasma, or platelet releasate VEGF. In univariate analysis, aspirin use attenuated the tamoxifen-associated increase in VEGF in the platelet releasate and decreased serum levels of VEGF (P = 0.03). Aromatase inhibitor therapy resulted in a decrease in serum endostatin concentrations (P = 0.04), whereas plasma concentrations of endostatin tended to be higher during treatment with aromatase inhibitors (P = 0.06). Tamoxifen therapy resulted in no change in serum or plasma endostatin concentrations. Platelet releasate concentrations of endostatin did not change with either treatment. Interindividual variability was noted among both aromatase inhibitor– and tamoxifen-treated patients. Conclusions: Tamoxifen and aromatase inhibitor therapy affect VEGF and endostatin levels and likely contribute to the angiogenic balance in breast cancer patients. Aspirin decreased the proangiogenic effects of tamoxifen, suggesting that antiplatelet and/or antiangiogenic therapy might improve the effectiveness of tamoxifen in women with breast cancer.

The minor allele of GP6 T13254C is associated with decreased platelet activation and a reduced risk of recurrent cardiovascular events and mortality: results from the SMILE–Platelets project

Summary.  Background: Contradictory results have been published on the effects of T13254C (rs1613662), which distinguishes the two major isoforms of GP6, the gene encoding the platelet receptor glycoprotein VI, on platelet function and the risk of cardiovascular disease. Methods: We performed a population‐based case–control study, the Study of Myocardial Infarctions in Leiden, among 547 male patients with a first myocardial infarction (MI) and 646 control subjects, as well as a prospective cohort study in which the same MI patients were followed for recurrent events (fatal and non‐fatal MI and unstable angina) and mortality (median follow‐up of 12 years). P‐selectin expression by platelets induced by crosslinked collagen‐related peptide (CRP‐XL) was measured by whole blood flow cytometry in 274 MI patients. Results: T13254C was not associated with a first MI, but seemed to be associated with a reduced incidence of recurrent events [per‐allele hazard ratio 0.77, 95% confidence interval (CI) 0.56–1.06] and mortality (hazard ratio 0.57, 95% CI 0.37–0.89). Pooling with the Heart and Estrogen/Progestin Replacement Study revealed hazard ratios of 0.81 (95% CI 0.66–0.99) and 0.73 (95% CI 0.55–0.96). The minor C‐allele was also strongly associated with a reduced percentage of P‐selectin‐expressing platelets. The reduction per C‐allele was 23% (95% CI 18–28%). In an independent study of 219 healthy volunteers, the per‐allele reduction of CRP‐XL‐induced aggregation was 10% (95% CI 2–18%). Conclusion: The minor allele of GP6 T13254C that reduced platelet activation and aggregation also seemed to be associated with a reduced incidence of recurrent cardiovascular events and mortality, but was not associated with first MI.

Efficacy of a short course of complex lymphedema therapy or graduated compression stocking therapy in the treatment of post-thrombotic syndrome

Treatment options for established post-thrombotic syndrome (PTS) are limited. Complex lymphedema therapy (CLT), a non-invasive treatment that improves lymphatic flow, may have the potential to improve PTS. We conducted a single-center, investigator-blind, randomized controlled trial of 31 patients with a clinically established diagnosis of PTS and compared the efficacy of graduated compression stockings alone (30–40 mmHg) with CLT, a treatment that includes compression stockings, exercise, patient education, skin care and lymphatic drainage. Primary outcomes were the 1- and 3-month changes in PTS severity by the Villalta score and disease-specific quality of life using the VEINES-QOL (Venous Insufficiency Epidemiological and Economic Study Quality of Life) questionnaire. Analysis was by intent-to-treat. We found from a baseline average score of 9.9 points, CLT reduced mean PTS severity scores by −2.4 points (p=0.02) at the 1-month and −2.3 points (p=0.05) at the 3-month follow-up. Score reductions with stockings only were similar at −2.1 (p=0.03) and −3.3 points (p=0.03) at 1 and 3 months. The differences in score between treatments were not significant. Neither treatment significantly changed the VEINES-QOL score except in patients with severe disease. Patients with moderate to severe PTS derived the greatest benefit from either therapy and the two therapies differentially impacted PTS signs and symptoms. We found a short course of lymphedema therapy and compression stockings offer similar benefit in patients with PTS; however, larger studies are needed to further explore the potential use of CLT in PTS, particularly in patients with more severe disease. ClinicalTrials.gov Identifier: NCT00633971.