Acromegaly and colorectal cancer: a comprehensive review of epidemiology, biological mechanisms, and clinical implications

Growth hormone excess and the development of growth hormone receptor antagonists

In 1990, a single amino acid substitution in the growth hormone (GH) gene at position 119 was found to transform the consequent protein from an agonist to an antagonist at the growth hormone receptor (GHR). Further amino acid substitutions plus prolongation of the half-life of the protein by pegylation resulted in the first clinically effective GHR antagonist, pegvisomant. Following extensive clinical trials, this medication has emerged as the most efficacious therapy for treatment-resistant acromegaly. Subsequent advances in our understanding of GH-GHR interactions and downstream GH signalling pathways suggest that pegvisomant binds to preformed GHR dimers and prevents rotational changes within the receptor-GH complex necessary for intracellular signalling to occur. This article reviews the discovery of pegvisomant, from initial experimental data to successful licensing of the drug for treatment-resistant acromegaly, and discusses its other potential therapeutic uses in diseases with abnormalities in the GH-IGF-I axis.

Acromegaly

Acromegaly is an acquired disorder related to excessive production of growth hormone (GH) and characterized by progressive somatic disfigurement (mainly involving the face and extremities) and systemic manifestations. The prevalence is estimated at 1:140,000-250,000. It is most often diagnosed in middle-aged adults (average age 40 years, men and women equally affected). Due to insidious onset and slow progression, acromegaly is often diagnosed four to more than ten years after its onset. The main clinical features are broadened extremities (hands and feet), widened thickened and stubby fingers, and thickened soft tissue. The facial aspect is characteristic and includes a widened and thickened nose, prominent cheekbones, forehead bulges, thick lips and marked facial lines. The forehead and overlying skin is thickened, sometimes leading to frontal bossing. There is a tendency towards mandibular overgrowth with prognathism, maxillary widening, tooth separation and jaw malocclusion. The disease also has rheumatologic, cardiovascular, respiratory and metabolic consequences which determine its prognosis. In the majority of cases, acromegaly is related to a pituitary adenoma, either purely GH-secreting (60%) or mixed. In very rare cases, acromegaly is due to ectopic secretion of growth-hormone-releasing hormone (GHRH) responsible for pituitary hyperplasia. The clinical diagnosis is confirmed biochemically by an increased serum GH concentration following an oral glucose tolerance test (OGTT) and by detection of increased levels of insulin-like growth factor-I (IGF-I). Assessment of tumor volume and extension is based on imaging studies. Echocardiography and sleep apnea testing are used to determine the clinical impact of acromegaly. Treatment is aimed at correcting (or preventing) tumor compression by excising the disease-causing lesion, and at reducing GH and IGF-I levels to normal values. Transsphenoidal surgery is often the first-line treatment. When surgery fails to correct GH/IGF-I hypersecretion, medical treatment with somatostatin analogs and/or radiotherapy can be used. The GH antagonist (pegvisomant) is used in patients that are resistant to somatostatin analogs. Adequate hormonal disease control is achieved in most cases, allowing a life expectancy similar to that of the general population. However, even if patients are cured or well-controlled, sequelae (joint pain, deformities and altered quality of life) often remain.

Does acromegaly enhance mortality?

The increased mortality associated with acromegaly was first demonstrated in early epidemiological studies. Since the seminal paper by Wright et al. in 1970, nearly 20 studies have analyzed mortality rates in over 5,000 patients with acromegaly. Overall standardized mortality rates are approximately two times higher than in the general population, relating to an average reduction in life expectancy of around 10 years. The excess deaths are due predominantly to cardiovascular, cerebrovascular and respiratory disease. Malignancy deaths have been high in some studies but not others; in the largest series looking at cancer mortality in acromegaly, overall cancer deaths were not increased, but colon cancer mortality was higher than expected. In 1993, Bates et al. first demonstrated that outcome was related to the latest measurable growth hormone (GH), and treatment to reduce GH levels led to improved outcomes. Other factors predicting poor outcome include the presence of hypertension and diabetes. On the basis of current evidence, a latest GH of less than 2-2.5 mug/L is a better predictor of good outcome than a normal insulin-like growth factor-1 (IGF-1), possibly due to discrepancy between GH and IGF-1 at low GH levels. There is some evidence to suggest a more stringent GH cut-off (less than 1 mug/L) may yield additional benefit but further studies are required to investigate any added risk of increased mortality from hypopituitarism. Radiotherapy has been linked specifically to cerebrovascular mortality and its use in patients with acromegaly must involve a careful risk-benefit analysis in each case.

Long-term endocrine sequelae of childhood cancer

PURPOSE OF REVIEW

To update knowledge related to the long-term endocrine sequelae of childhood cancer.

RECENT FINDINGS

Endocrine deficiencies are common after cranial irradiation, chemotherapy and specific tumors. These deficiencies include growth hormone, thyrotropin, adrenocorticotropin and gonadotropin deficiencies, primary hypothyroidism, gonadal failure and obesity. Recent studies highlight the impact of radiation on the development of endocrine sequelae. Risks for obesity after childhood tumors include hypothalamic injury, with inactivity and daytime sleepiness. About 6% of adult female survivors of childhood cancer develop persistent ovarian failure. Risks for ovarian damage include ovarian irradiation and alkylating agents. Appropriate fertility-preservation options should be offered. Offspring of women who had uterine irradiation as children are more likely to be born preterm or have low birth weight. Secondary neoplasia or relapse should be considered when treating endocrine deficiencies in cancer survivors. Risk of secondary neoplasia is increased following radiation exposure and certain malignancies. Treatment with growth hormone does not increase cancer recurrence, but survivors may have a 2-fold risk of developing a secondary solid tumor, most commonly a meningioma.

SUMMARY

Standardized, multidisciplinary long-term surveillance is important in childhood cancer survivors to identify and treat endocrine and other late effects of cancer and its therapy.

Plasma C-peptide, insulin-like growth factor-I, insulin-like growth factor binding proteins and risk of colorectal cancer in a nested case-control study: the Japan public health center-based prospective study

The physical inactivity and obesity involved in hyperglycemia and hyperinsulinemia is supposed to lead to an increased bioavailability of insulin-like growth factor-I (IGF-I). The carcinogenic effect of IGF-I may be influenced by IGF binding proteins. We investigated the association between plasma levels of C-peptide, a surrogate biomarker of insulin, IGFBP-1, IGF-I or IGFBP-3, and the risk of colorectal cancer in a nested case-control study. During an 11.5-year follow-up, 375 newly diagnosed colorectal cancers were identified in a cohort of 38,373 adults who had returned the baseline questionnaire and provided blood samples. Two matched-controls for each case were selected from the cohort. The odds ratio (OR) of colorectal cancer for plasma levels of each protein was estimated using the conditional logistic regression model adjusted for potential confounding factors. We observed a statistically significant association of plasma C-peptide with colorectal cancer only in men. The ORs were 1.0, 2.3, 2.8 and 3.2 along with quartiles (p trend, 0.0072). The association was stronger in colon cancer (p trend, 0.025) than in rectal cancer (p trend, 0.24). Other peptides were not associated with the risk in either men or women. The results did not change when repeatedly analyzed by tumor invasion levels, tumor sites or follow-up periods. In conclusion, a higher plasma C-peptide may indicate a subsequent risk of colorectal cancer in Japanese men.

Growth hormone and its disorders

Growth hormone (GH) is synthesised and secreted by the somatotroph cells of the anterior lobe of the pituitary gland. Its actions involve multiple organs and systems, affecting postnatal longitudinal growth as well as protein, lipid, and carbohydrate metabolism. GH hypersecretion results in gigantism or acromegaly, a condition associated with significant morbidity and mortality, while GH deficiency results in growth retardation in children and the GH deficiency syndrome in adults. This article, aimed at non-paediatric physicians, examines the clinical features, diagnosis, and current concepts in the management of these conditions.

Body size and risk of colon and rectal cancer in the European Prospective Investigation Into Cancer and Nutrition (EPIC)

BACKGROUND

Body weight and body mass index (BMI) are positively related to risk of colon cancer in men, whereas weak or no associations exist in women. This discrepancy may be related to differences in fat distribution between sexes or to the use of hormone replacement therapy (HRT) in women.

METHODS

We used multivariable adjusted Cox proportional hazards models to examine the association between anthropometric measures and risks of colon and rectal cancer among 368 277 men and women who were free of cancer at baseline from nine countries of the European Prospective Investigation Into Cancer and Nutrition. All statistical tests were two-sided.

RESULTS

During 6.1 years of follow-up, we identified 984 and 586 patients with colon and rectal cancer, respectively. Body weight and BMI were statistically significantly associated with colon cancer risk in men (highest versus lowest quintile of BMI, relative risk [RR] = 1.55, 95% confidence interval [CI] = 1.12 to 2.15; P(trend) = .006) but not in women. In contrast, comparisons of the highest to the lowest quintile showed that several anthropometric measures, including waist circumference (men, RR = 1.39, 95% CI = 1.01 to 1.93; P(trend) = .001; women, RR = 1.48, 95% CI = 1.08 to 2.03; P(trend) = .008), waist-to-hip ratio (WHR; men, RR = 1.51, 95% CI = 1.06 to 2.15; P(trend) = .006; women, RR = 1.52, 95% CI = 1.12 to 2.05; P(trend) = .002), and height (men, RR = 1.40, 95% CI = 0.99 to 1.98; P(trend) = .04; women, RR = 1.79, 95% CI = 1.30 to 2.46; P(trend)<.001) were related to colon cancer risk in both sexes. The estimated absolute risk of developing colon cancer within 5 years was 203 and 131 cases per 100,000 men and 129 and 86 cases per 100,000 women in the highest and lowest quintiles of WHR, respectively. Upon further stratification, no association of waist circumference and WHR with risk of colon cancer was observed among postmenopausal women who used HRT. None of the anthropometric measures was statistically significantly related to rectal cancer.

CONCLUSIONS

Waist circumference and WHR, indicators of abdominal obesity, were strongly associated with colon cancer risk in men and women in this population. The association of abdominal obesity with colon cancer risk may vary depending on HRT use in postmenopausal women; however, these findings require confirmation in future studies.

Haplotype insufficiency for suppressor of cytokine signaling-2 enhances intestinal growth and promotes polyp formation in growth hormone-transgenic mice

GH may improve intestinal growth or function in patients with short bowel syndrome. Excessive trophic effects of GH or IGF-I may contribute to neoplastic growth or increased colorectal cancer risk in acromegaly. Identification of mechanisms that limit the tumorigenic potential of GH and IGF-I is desirable. Suppressor of cytokine signaling-2 (SOCS2) limits GH action on body and organ growth, but its role in GH action on intestine is unknown. We tested the hypothesis that SOCS2 limits GH-induced intestinal growth or neoplasia in vivo. GH-transgenic (GH-TG) mice were crossed with SOCS2 null mice to generate wild-type (WT) or transgenic (TG) mice with zero (HO-WT; HO-TG), one (HT-WT; HT-TG), or two (WT-WT; WT-TG) functional SOCS2 genes. No HO-TG mice were derived from crossbreeding. WT-WT, HT-WT, WT-TG, and HT-TG were compared. Body weight, small intestine and colon growth, and levels of jejunal IGF-I and sucrase-isomaltase mRNAs were assessed. Colon was analyzed for abnormal lesions. HT-WT did not differ from WT-WT. Compared with WT-TG, HT-TG had significantly increased body weight, small intestine growth, and local IGF-I expression and decreased sucrase-isomaltase expression. HT-TG colon spontaneously developed multiple hyperplastic and lymphoid polyps. GH-induced activation of STAT5 DNA binding activity was enhanced in intestine of SOCS2 null mice compared with WT control. Haplotype insufficiency for SOCS2 promotes trophic actions of GH in small intestine and promotes preneoplastic growth in colon during excess GH. Small variations in SOCS2 expression levels may significantly influence the outcome of therapeutic GH or acromegaly in intestine.

The insulin-like growth factor system and colorectal cancer: clinical and experimental evidence

OBJECTIVE

The aim of this review is to clarify the involvement of the insulin-like growth factor (IGF) system in the development of colorectal malignancy.

MATERIALS AND METHODS

Medline searches were used to identify key articles relating the IGF system with the development of colorectal cancer.

RESULTS

The IGF system has been linked to colorectal malignancy by a convergence of data from epidemiological, clinical and laboratory-based sources.

CONCLUSION

Further work is needed to characterise the IGF system expression in the colon. Such clarification could lead to the identification of targets that can be manipulated for clinical advantage.

Does growth hormone cause cancer?

The ability of GH, via its mediator peptide IGF-1, to influence regulation of cellular growth has been the focus of much interest in recent years. In this review, we will explore the association between GH and cancer. Available experimental data support the suggestion that GH/IGF-1 status may influence neoplastic tissue growth. Extensive epidemiological data exist that also support a link between GH/IGF-1 status and cancer risk. Epidemiological studies of patients with acromegaly indicate an increased risk of colorectal cancer, although risk of other cancers is unproven, and a long-term follow-up study of children deficient in GH treated with pituitary-derived GH has indicated an increased risk of colorectal cancer. Conversely, extensive studies of the outcome of GH replacement in childhood cancer survivors show no evidence of an excess of de novo cancers, and more recent surveillance of children and adults treated with GH has revealed no increase in observed cancer risk. However, given the experimental evidence that indicates GH/IGF-1 provides an anti-apoptotic environment that may favour survival of genetically damaged cells, longer-term surveillance is necessary; over many years, even a subtle alteration in the environmental milieu in this direction, although not inducing cancer, could result in acceleration of carcinogenesis. Finally, even if GH/IGF-1 therapy does result in a small increase in cancer risk compared to untreated patients with GH deficiency, it is likely that the eventual risk will be the same as the general population. Such a restoration to normality will need to be balanced against the known morbidity of untreated GH deficiency.

Colorectal neoplasm and acromegaly

The risk for colorectal carcinoma in acromegaly remains controversial. In our earlier study, we have demonstrated that the risk of colorectal carcinoma in Asian Indians with acromegaly is not increased and after this report, routine colonoscopy in our patients with acromegaly was abandoned. Subsequently, two consecutive young men aged 30 and 35, one 6 years after and other at the time of diagnosis of acromegaly had colorectal carcinoma respectively. None of them had family history of colonic neoplasm. These two younger patients with no other predisposition for colorectal neoplasm suggests that colonoscopy should be done in all patients with acromegaly at diagnosis and they should remain under surveillance.

Insulin resistance, apoptosis, and colorectal adenoma risk

Compelling evidence from epidemiologic studies indicates that elevated circulating insulin-like growth factor (IGF)-I, insulin resistance, and associated complications, such as elevated fasting plasma insulin, glucose and free fatty acids, glucose intolerance, increased body mass index, and visceral adiposity, are linked with increased risk of colorectal cancer. However, the role of insulin and markers of glucose control in the development of adenomas, precursors to colorectal cancer, has not been fully explored. We evaluated the relationship between plasma insulin, glucose, IGF-I, IGF-II, IGF-binding protein-3 (IGFBP-3), apoptosis, and colorectal adenomas in a case-control study. Participants were drawn from consenting patients undergoing colonoscopy at the University of North Carolina hospitals (Chapel Hill, NC). Participants were classified as cases or controls based on whether they had one or more colorectal adenomatous polyps. Fasting plasma insulin, IGF-I, IGF-II, and IGFBP-3 levels were assessed by ELISA. Glucose was measured by glucose hexokinase assay. Apoptosis was assessed by morphology on H&E-stained sections. Dietary and lifestyle information were obtained by telephone interview. Logistic regression was used to examine the association between adenoma status and insulin-IGF markers. Adenoma cases (n = 239) and adenoma-free controls (n = 517) provided rectal biopsies and/or blood samples and interview data. Consistent with prior findings, cases were more likely to be males, older, have higher waist-to-hip ratio, lower calcium intake, lower apoptosis, and less likely to report nonsteroidal anti-inflammatory drug use. Those in the highest quartile of insulin (adjusted odds ratio, 2.2; 95% confidence interval, 1.1-4.2) and glucose (adjusted odds ratio, 1.8; 95% confidence interval, 0.9-3.6) were more likely to have an adenoma compared with the lowest quartile. Similarly, subjects in the highest two quartiles of insulin were more likely to be in the lowest two quartiles of apoptosis. Overall, there were no significant differences between mean circulating levels of glucose, IGF-I, IGF-II, and IGFBP-3 among cases and controls and no association between these variables and apoptosis. The results provide novel evidence that elevated insulin and glucose are associated with increased adenoma risk and decreased apoptosis in normal rectal mucosa. These findings suggest that insulin may act early in the adenoma-carcinoma sequence to promote the development of colorectal adenoma by decreasing apoptosis in the normal mucosa.

Recombinant Human Insulin-Like Growth Factor I (IGF-I): Risks and Benefits of Normalizing Blood IGF-I Concentrations

Recombinant human (rh) insulin-like growth factor I (IGF-I) is being developed as a therapy for short stature caused by IGF deficiency (IGFD) and also for diabetes mellitus. To complement the human efficacy and safety data, a large amount of information is available regarding the pharmacology and toxicology of rhIGF-I in animals. This review summarizes the risks and benefits of normalizing blood IGF-I concentrations in IGFD, especially with regard to carcinogenicity, and compares and contrasts safety data for rhIGF-I, recombinant human growth hormone (rhGH), and insulin. A major difference between rhIGF-I and rhGH is that rhIGF-I (like insulin) has hypoglycaemic activity, whereas rhGH opposes insulin action and is diabetogenic. In most of their actions, GH and IGF-I are similar. IGF-I mediates most of the actions of GH, so the safety of rhGH and that of rhIGF-I also share many common features. In animals, the transgenic expression of hGH has been shown to act directly, by activating the prolactin receptor, to increase the incidence of mammary and prostate tumours. In comparison, the over-expression of IGF-I in animals or the administration of rhIGF-I does not have a carcinogenic effect. In formal toxicology and carcinogenicity studies, rhIGF-I has similar effects to insulin in that it can increase food intake, body size, and the growth rate of existing tumours. In animals and humans, IGFD has many long-term detrimental effects besides short stature: it increases the risk of diabetes, cardiovascular disease, and low bone mineral density. Therefore, a case can be made for replacement therapy with rhIGF-I to normalize blood IGF-I levels and reverse the detrimental effects of IGFD.

Determination of large bowel length and loop complexity in patients with acromegaly undergoing screening colonoscopy

BACKGROUND

Patients with acromegaly are at moderately increased risk of developing colorectal cancer and may be considered for screening colonoscopy. In turn, large bowel dimensions may be increased in these patients, factors that predict for increased risk of serious complications such as perforation.

OBJECTIVE

To evaluate this risk potential, we measured large bowel length and loop complexity using magnetic endoscopic imaging (MEI).

DESIGN

Case-control study in 25 unselected patients with acromegaly (mean age 56 years) vs. 41 nonacromegalic controls (mean age 60 years) undergoing screening colonoscopy.

MEASUREMENTS

MEI parameters were determined and age- and sex-adjusted mean differences calculated. The dependency of total large bowel length on various demographic and disease-related factors (e.g. GH exposure, IGF-I and IGFBP-3 concentrations) was assessed using regression techniques.

RESULTS

Total large bowel length was increased by 20%[95% confidence interval (CI) 9-31%] in patients with acromegaly compared with controls (unadjusted and adjusted; P-values < 0.001). Acromegaly was also associated with increased time taken to reach the caecum (P = 0.01) and increased pelvic loop complexities (5/25 vs. 1/41, Fisher's exact test: P = 0.03). Total large bowel length was predicted by age at colonoscopy (P = 0.003) and patient height (P = 0.03), but not by surrogate biochemical markers of disease activity.

CONCLUSIONS

Acromegaly is associated with increased large bowel length and loop complexity making colonoscopy technically challenging, and theoretically increasing the risk of serious complications. Patients need to be counselled accordingly, and appropriate resources with experienced staff allocated.

Clinical effects of growth hormone on bone: a review

Growth hormone (GH) stimulates bone turnover. Deficiency of GH due to hypopituitarism is related to low bone mineral density and increased fracture risk. GH substitution increases and thus normalizes bone mineral density in these patients, which is one of a number of arguments for GH substitution in hypopituitarism. In contrast, a possible therapeutic use of GH in idiopathic osteoporosis and glucocorticoid-induced osteoporosis is speculative and not established. Reduction of osteoporosis risk is an argument brought up for a use of GH in healthy elderly persons (anti-aging medicine). However, since only very limited data are available yet, this cannot be based on scientific evidence, and there are important concerns about the safety of use of GH in healthy elderly persons.

Advances in Growth Hormone Therapy: A New Registry Tool

Growth hormone (GH) deficiency is a rare condition, and physicians may lack clinical experience of its treatment. Despite evidence for the efficacy and tolerability of GH therapy, a substantial proportion of patients remain untreated. Registries and other large-scale databases are an important tool for expanding the evidence base for GH treatment. Since the mid-1980s, registries have provided data on important aspects of the safety and efficacy of GH treatment. Registries have also allowed pooling of data from patients with rare conditions that could otherwise not be recruited in sufficient numbers for clinical trials. Importantly for patients and their relatives, use of registry data has allowed the development of prediction models that indicate the likely outcomes of treatment. MEGHA (Metabolic Endocrinology and Growth Hormone Assessment) is a recently developed, observational database with a number of features not found in existing registries, including its use as a day-to-day clinical management tool, the ability to create individual sub-studies, direct comparison of personal data against the full database, and a particular focus on the transition from childhood to adulthood. This creative registry is a promising instrument for further research into GH-related disorders that will improve GH therapy and thus provide benefits for patients.