Epidemiologic studies suggest that type 2 diabetes (T2D) increases breast cancer risk and mortality, but there is limited experimental evidence supporting this association. Moreover, there has not been any definition of a pathophysiological pathway that diabetes may use to promote tumorigenesis. In the present study, we used the MKR mouse model of T2D to investigate molecular mechanisms that link T2D to breast cancer development and progression. MKR mice harbor a transgene encoding a dominant-negative, kinase-dead human insulin-like growth factor-I receptor (IGF-IR) that is expressed exclusively in skeletal muscle, where it acts to inactivate endogenous insulin receptor (IR) and IGF-IR. Although lean female MKR mice are insulin resistant and glucose intolerant, displaying accelerated mammary gland development and enhanced phosphorylation of IR/IGF-IR and Akt in mammary tissue, in the context of three different mouse models of breast cancer, these metabolic abnormalities were found to accelerate the development of hyperplastic precancerous lesions. Normal or malignant mammary tissue isolated from these mice exhibited increased phosphorylation of IR/IGF-IR and Akt, whereas extracellular signal-regulated kinase 1/2 phosphorylation was largely unaffected. Tumor-promoting effects of T2D in the models were reversed by pharmacological blockade of IR/IGF-IR signaling by the small-molecule tyrosine kinase inhibitor BMS-536924. Our findings offer compelling experimental evidence that T2D accelerates mammary gland development and carcinogenesis,and that the IR and/or the IGF-IR are major mediators of these effects. Cancer Res; 70(2); 741–51

The growth-promoting actions of growth hormone were originally hypothesized to be mediated through a circulating liver-generated sulfation factor that later came to be known as insulin-like growth factor I (IGF-I).¹ This growth factor is produced in almost every tissue in the body.² In the cartilage growth plate, growth hormone–induced IGF-I³ acts locally through autocrine–paracrine mechanisms.⁴

Obesity increases the risk of many cancers in both males and females. This study describes a link between obesity, obesity-associated metabolic alterations, and the risk of developing cancer in male and female mice. The goal of this study was to evaluate the relationship between gender and obesity and to determine the role of estrogen status in obese females and its effect on tumor growth. We examined the susceptibility of C57BL/6 mice to diet-induced obesity, insulin resistance/glucose intolerance, and tumors. Mice were injected sc with one of two tumorigenic cell lines, Lewis lung carcinoma, or mouse colon 38-adenocarcinoma. Results show that tumor growth rate was increased in obese mice vs. control mice irrespective of the tumor cell type. To investigate the effect of estrogen status on tumor development in obese females, we compared metabolic parameters and tumor growth in ovariectomized (ovx) and intact obese female mice. Obese ovx female mice developed insulin resistance and glucose intolerance similar to that observed in obese males. Our results demonstrate that body adiposity increased in ovx females irrespective of the diet administered and that tumor growth correlated positively with body adiposity. Overall, these data point to more rapid tumor growth in obese mice and suggest that endogenous sex steroids, together with diet, affect adiposity, insulin sensitivity, and tumor growth in female mice.

Growth hormone (GH) has been used for over 35 years, and its safety and efficacy has been studied extensively. Experimental studies showing the permissive role of GH/insulin-like growth factor 1 (IGF-I) in carcinogenesis have raised concerns regarding the safety of GH replacement in children and adults who have received treatment for cancer and those with intracranial and pituitary tumours. A consensus statement was produced to guide decision-making on GH replacement in children and adult survivors of cancer, in those treated for intracranial and pituitary tumours and in patients with increased cancer risk. With the support of the European Society of Endocrinology, the Growth Hormone Research Society convened a Workshop, where 55 international key opinion leaders representing 10 professional societies were invited to participate. This consensus statement utilized: (1) a critical review paper produced before the Workshop, (2) five plenary talks, (3) evidence-based comments from four breakout groups, and (4) discussions during report-back sessions. Current evidence reviewed from the proceedings from the Workshop does not support an association between GH replacement and primary tumour or cancer recurrence. The effect of GH replacement on secondary neoplasia risk is minor compared to host- and tumour treatment-related factors. There is no evidence for an association between GH replacement and increased mortality from cancer amongst GH-deficient childhood cancer survivors. Patients with pituitary tumour or craniopharyngioma remnants receiving GH replacement do not need to be treated or monitored differently than those not receiving GH. GH replacement might be considered in GH-deficient adult cancer survivors in remission after careful individual risk/benefit analysis. In children with cancer predisposition syndromes, GH treatment is generally contraindicated but may be considered cautiously in select patients.

Serum insulin‐like growth factor (IGF) ‐1 is secreted mainly by the liver and circulates bound to IGF‐binding proteins (IGFBPs), either as binary complexes or ternary complexes with IGFBP‐3 or IGFBP‐5 and an acid‐labile subunit (ALS). The purpose of this study was to genetically dissect the role of IGF‐1 circulatory complexes in somatic growth, skeletal integrity, and metabolism. Phenotypic comparisons of controls and four mouse lines with genetic IGF‐1 deficits— liver‐specific IGF‐1 deficiency (LID), ALS knockout (ALSKO), IGFBP‐3 (BP3) knockout, and a triply deficient LID/ALSKO/BP3 line—produced several novel findings. 1 ) All deficient strains had decreased serum IGF‐1 levels, but this neither predicted growth potential or skeletal integrity nor defined growth hormone secretion or metabolic abnormalities. 2 ) IGF‐1 deficiency affected development of both cortical and trabecular bone differently, effects apparently dependent on the presence of different circulating IGF‐1 complexes. 3 ) IGFBP‐3 deficiency resulted in increased linear growth. In summary, each IGF‐1 complex constituent appears to play a distinct role in determining skeletal phenotype, with different effects on cortical and trabecular bone compartments.— Yakar, S., Rosen, C. J., Bouxsein, M. L., Sun, H., Mejia, W., Kawashima, Y., Wu, Y., Emerton, K., Williams, V., Jepsen, K., Schaffler, M. B., Majeska, R. J., Gavrilova, O., Gutierrez, M., Hwang, D., Pennisi, P., Frystyk, J., Boisclair, Y., Pintar, J., Jasper, H., Domene, H., Cohen, P., Clemmons, D., LeRoith, D. Serum complexes of insulin‐like growth factor‐1 modulate skeletal integrity and carbohydrate metabolism. FASEB J. 23, 709–719 (2009)

GH and IGF-I are potent regulators of muscle growth and function. Although IGF-I is known to mediate many of the effects of GH, it is not yet clear whether all effects of GH are completely dependent on the IGF-I system. To evaluate the biological effects of the GH/IGF-I axis on muscle growth, we administrated recombinant human GH to mice, which lack IGF-I function specifically in skeletal muscle, due to the overexpression of a dominant-negative IGF-I receptor in this tissue (MKR mice). GH treatment significantly increased the levels of hepatic IGF-I mRNA and serum IGF-I levels in both wild-type (WT) and MKR mice. These GH-induced effects were paralleled by increases in body weight and in the weights of most GH-responsive organs in both groups of mice. Interestingly, unlike WT mice, GH treatment had no effect on skeletal muscle weight in MKR mice. GH treatment failed to reverse the impaired muscle function in MKR mice. Furthermore, MKR mice exhibited no effects of GH on the cross-sectional area of myofibers and the proliferation of satellite cells. Taken together, these data suggest that the in vivo effects of GH on muscle mass and strength are primarily mediated by activation of the IGF-I receptor.